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How to Fix Windows Stop Code 0xc000021a (Full Expert Guide)

0xc000021a is a Blue Screen of Death error that can occur on Windows 10, 8.1, 8, 7, Vista, and XP. It’s also known as STOP 0xC000021A, STATUS_SYSTEM_PROCESS_TERMINATED, HALT: c000021a {Fatal System Error}, and STOP c000021a. On Windows 10, it’s accompanied by the Your PC ran into a problem and needs to restart message.

Many users report getting this stop code after upgrading Windows 10 to a newer edition. It usually shows up on the screen when trying to boot to Windows, making it challenging to fix this BSOD error by just relying on the tools available in BIOS and Advanced Startup mode.

Because of this, you might be tempted to turn to a professional for help. But it’s not necessary for fixing a problem similar to the Inaccessible Boot Device error, as long as you follow the simple instructions below.

Windows Stop Code 0xc000021a

How to fix 0xc000021a BSOD error on Windows 10

Windows stop code 0xc000021a can be caused by Winlogon.exe (Windows Logon Subsystem) or Csrss.exe (Client/Server Runtime Subsystem) if any of these core components stop working properly. In this case, you have to fix the malfunctioning processes.

1. Start Windows 10 in Safe Mode with Networking

If you can’t boot your operating system due to the 0xc000021a error, try to start Windows 10 in Safe Mode with networking features. It’s a secure booting environment that disables all optional drivers, services, and processes that might be causing this problem. Here’s what you need to do:

  1. Interrupt the boot sequence three times in a row to launch Windows troubleshooting
  2. Select Troubleshoot > Advanced options > Startup SettingsWindows 10 shows the advanced startup options
  3. Click Restart and wait a few seconds
  4. Press F5 to enable Safe Mode with Networking

Windows 10 should start now. If it doesn’t, return to Startup Settings and press F4 to enable Safe Mode without networking features.

2. Clean boot Windows 10

If Safe Mode was successful, you can run a clean Windows 10 boot to make the changes permanent, at least until you get the chance to thoroughly troubleshoot the 0xc000021a error.

  1. Start Windows 10 in Safe Mode
  2. Press Win key + R, type msconfig, and press Enter to open the System Configuration app
  3. Select the General tab
  4. Pick Selective Startup
  5. Uncheck the Load system services and Load startup items boxes
  6. Click Apply
  7. Switch to the Startup tab
  8. Click Open Task ManagerWindows 10 shows how to open Task Manager from the System Configuration app
  9. Select an app with the Enabled status and click Disable. Do this for all enabled appsWindows 10 shows how to disable startup processes
  10. Restart your computer

3. Run Startup Repair

You can troubleshoot the errors that prevent your operating system from booting by running the Startup Repair tool in the troubleshoot menu before boot. However, you need to use your Windows 10 installation disc. If you don’t have it, you can use another computer to create one.

How to create Windows 10 installation media (on a working PC):

  1. Connect a USB flash drive and make sure to copy any files you might need later since the drive will be formatted
  2. Download Media Creation Tool from the official website
  3. Launch the application and follow the instructions

How to run Startup Repair (on the malfunctioning PC):

  1. Plug the USB flash drive into the PC
  2. Turn your PC on and off three times to reach the Advanced Startup menu
  3. Select Troubleshoot > Advanced options > Startup Repair
  4. Choose your PC account and enter your password to continue
  5. Follow the step-by-step instructions

4. Disable Driver Signature Enforcement

By default, Windows doesn’t allow unsigned drivers to run on your PC. So, if you have recently installed drivers from third-party sources, your operating system won’t boot due to Driver Signature Enforcement. In turn, this leads to the 0xc000021a error.

But you can fix this by disabling Driver Signature Enforcement:

  1. Force Windows to load the troubleshooting screen (interrupt the boot sequence three times)
  2. Go to Troubleshoot > Advanced options > Startup Settings
  3. Click Restart
  4. Press F7 to disable Driver Signature Enforcement
  5. Try to start Windows 10 now

If it doesn’t work, you can use Command Prompt:

  1. Select Troubleshoot > Advanced options > Command Prompt
  2. Choose your account and enter your password to continue
  3. Run bcdedit /set testsigning on. If it displays the The operation completed successfully message, try to boot Windows 10. But if it says Protected by Secure Boot policy, you must turn off Secure Boot from the UEFI firmware

How to disable Secure Boot from the UEFI firmware settings:

  1. In the troubleshooting menu, go to Troubleshoot > UEFI Firmware Settings
  2. Click Restart
  3. After accessing BIOS, select the Authentication section
  4. Set Secure Boot to Disabled
  5. Save the BIOS settings and exit. You can now run the bcdedit /set testsigning on command in Command Prompt

If you need to re-enable Driver Signature Enforcement, run Command Prompt again and use the bcdedit /set testsigning off command.

5. Fix hard drive corruption

Hard disk failure could cause problems with the Winlogon.exe and Csrss.exe processes, resulting in error 0xc000021a. But you can fix HDD errors using CHKDSK (Check Disk) from the console environment.

  1. Boot your computer to the troubleshooting menu
  2. Go to Troubleshoot > Advanced options > Command Prompt
  3. Select your account and enter your password to continue
  4. If Windows is installed on the C: drive, run chkdsk c: /f /r. Otherwise, make sure to replace c: with the correct partition letter
    • If you’re not sure where Windows is, select a drive letter (e.g. run c:) and list its directories (e.g. run dir). Do this for multiple drive letters until you spot the Windows folder

6. Repair corrupt system files

To repair corrupt operating files such as Winlogon.exe and Csrss.exe, you can turn to SFC (System File Checker):

  1. In the troubleshoot menu, visit Troubleshoot > Advanced options > Command Prompt
  2. Pick your PC account and input your password to continue
  3. Run sfc /scannow and wait
  4. It might be necessary to insert a Windows 10 installation media to restore system files

If SFC is unsuccessful, you can use DISM (Deployment Image Servicing and Management) to verify the component store of the Windows image:

  1. Make sure your PC is connected to the Internet
  2. In Command Prompt, run DISM /online /cleanup-image /scanhealth
  3. If DISM finds any errors, fix them by running DISM /online /cleanup-image /restorehealth
  4. Run SFC (sfc /scannow) again

7. Update old drivers

If you have never updated your drivers or haven’t done so for a long time, it could be the reason why you keep getting the 0xc000021a error before Windows boot. But you should be able to solve this problem by using a driver update tool in Safe Mode. Or, you can update drivers without having to install any third-party applications:

  1. Start Windows 10 in Safe Mode with Networking
  2. After the system boots, right-click the Start button and select Device ManagerWindows 10 shows how to access Device Manager from the Start right-click menu
  3. Double-click a device to access its properties
  4. Switch to the Driver tab and inspect the Driver Date. If it’s older than one year, check for updates by clicking the Update Driver buttonWindows 10 shows how to update the display driver
  5. Click Search automatically for drivers. Do this for all outdated driversWindows 10 shows how to search automatically for display drivers

If you get the The best drivers for your device are already installed message for any driver, click Search for updated drivers on Windows Update. You just have to do this once since Windows Update should download and install all available drivers.

On the other hand, if Windows can’t find a newer driver, you can visit the website of your device manufacturer to download the newest driver. Make sure to get drivers that are compatible with your devices and operating system. Then, retrace the steps above but choose Browse my computer for drivers to perform a manual installation.

8. Roll back incompatible drivers

Unsupported drivers can cause serious problems on your computer, including blue screen errors like 0xc000021a. After disabling Driver Signature Enforcement (see Solution 4), you should roll back these malfunctioning drivers to be able to update them correctly.

  1. Start Windows 10 in Safe Mode with Networking
  2. Press Win key + R, type devmgmt.msc, and press Enter to open Device Manager
  3. Extend all categories and look for any devices with a yellow exclamation mark
  4. Double-click the device and select the Driver tab
  5. Click Roll Back Driver and follow the instructions. If the Roll Back Driver is greyed out, you can’t perform the rollback because no previous driver is saved on your computer.The Roll Back Driver button is greyed out in Device Manager

9. Repair the system registry

The Windows registry could have corrupt entries that are essential for system boot. However, you can restore the registry to its default configuration from the command-line environment before boot.

  1. Interrupt the boot sequence three times to trigger the Advanced Startup menu
  2. Select Troubleshoot > Advanced options > Command Prompt
  3. Choose your account and enter your password to continue
  4. Type the following commands (press Enter after each line of text):
    • cd %SystemRoot%System32\config
    • ren %SystemRoot%System32\config\DEFAULT DEFAULT.old
    • ren %SystemRoot%System32\config\SAM SAM.old
    • ren %SystemRoot%System32\config\SECURITY SECURITY.old
    • ren %SystemRoot%System32\config\SOFTWARE SOFTWARE.old
    • ren %SystemRoot%System32\config\SYSTEM SYSTEM.old
    • copy %SystemRoot%System32\config\RegBack\DEFAULT %SystemRoot%System32\config\
    • copy %SystemRoot%System32\config\RegBack\DEFAULT %SystemRoot%System32\config\
    • copy %SystemRoot%System32\config\RegBack\SAM %SystemRoot%System32\config\
    • copy %SystemRoot%System32\config\RegBack\SECURITY %SystemRoot%System32\config\
    • copy %SystemRoot%System32\config\RegBack\SYSTEM %SystemRoot%System32\config\
    • copy %SystemRoot%System32\config\RegBack\SOFTWARE %SystemRoot%System32\config\
  5. Try to boot Windows now

10. Fix BCD

The BCD (Boot Configuration Data) is responsible for the Windows 10 startup operation. It it’s damaged in any way, it’s no wonder that your computer screen turns blue and shows the 0xc000021a error. But you can fix the BCD from Command Prompt:

  1. In the troubleshooting menu, go to Troubleshoot > Advanced options > Command Prompt
  2. Select your account and use your password to continue
  3. Write the next commands (press Enter after each one):
    • bootrec /repairbcd
    • bootrec /osscan
    • bootrec /repairmbr
  4. Exit Command Prompt and try to boot Windows 10

11. Uninstall third-party apps

You might have installed third-party software applications that don’t support your operating system or which conflict with each other. For instance, two antivirus solutions with distinct real-time engines are likely to clash and cause blue screen errors. To solve this problem, you just have to uninstall any programs added to your PC lately:

  1. Start Windows 10 in Safe Mode
  2. Right-click the Start button and go to Apps and FeaturesWindows 10 shows how to access Apps and Features from the Start right-click menu
  3. Set Sort by to Install date to view the latest programs firstWindows 10 shows how to sort apps by install date
  4. Select the first app in the list, click Uninstall, and again to confirmWindows 10 shows how to uninstall a program
  5. Do this for all programs recently installed
  6. Try to boot your OS normally now

12. Uninstall system updates

Not only software applications but also malfunctioning system updates can be dangerous for your computer. You can remove them before boot:

  1. Interrupt the boot sequence three times by turning your PC off and on
  2. When it shows the Advanced Startup screen, visit Troubleshoot > Advanced options > Uninstall Updates
  3. Select and uninstall the most recent Windows update
  4. Try to boot your operating system now

13. Unplug external devices

If you have recently attached new devices to your computer, such as a Wi-Fi adapter, a webcam, a printer, or a USB pen drive, there could be compatibility issues that result in BSOD errors like 0xc000021a. It can even happen with plug-and-play devices.

But you should be able to fix this by removing the USB cables from your PC. It’s also a good idea to change the USB ports in case some of them are not working correctly.

14. Reset BIOS

An incorrect BIOS configuration could be fatal for your computer. If you or someone else with access to your PC has accessed BIOS mode in order to enable overclocking, shadowing, caching, or something else, you should restore the BIOS configuration to default to remain on the safe side.

  1. In the troubleshooting menu, select Troubleshoot > Advanced Options > UEFI Firmware Settings
  2. Click Restart to enter BIOS mode
  3. Locate the option that resets your BIOS configuration data to default and turn it onhow to reset BIOS configuration data
  4. Save the new BIOS settings and exit
  5. Try to boot Windows 10

15. Update BIOS

BIOS needs to be regularly updated, just like software applications or your operating system. If you have never done this, you should get on it right away. But you need to use a pen drive and a working computer to download the BIOS installation files. Here are the complete steps:

  1. On your malfunctioning PC, reach the Advanced Startup menu (turn the PC off and on three times)
  2. Go to Troubleshoot > Advanced Options > UEFI Firmware Settings
  3. Click Restart to reach the BIOS setup mode
  4. In the main section, write down the BIOS manufacturer, current version, and install date
  5. Shift your attention to the working PC. Connect a USB flash drive
  6. Visit the manufacturer’s website and find a newer BIOS version by comparing it to the BIOS current version and install date
  7. Download the BIOS setup file and unzip the archive to the pen drive
  8. Disconnect the USB flash drive and plug it into the malfunctioning PC
  9. Follow the steps above to access the BIOS menu
  10. Create a backup of the current BIOS version
  11. Start the BIOS update and follow the steps
  12. Try to boot Windows after the update is complete

16. Disable Fast Boot

Fast Boot preloads the Windows drivers in order to boot your PC faster. But it’s known to sometimes cause Blue Screen of Death errors, so it’s a good idea to deactivate Fast Boot. Here’s what you need to do:

  1. Boot Windows 10 to the troubleshoot menu
  2. Select Troubleshoot > Advanced Options > UEFI Firmware Settings
  3. Click Restart
  4. Access the advanced BIOS options
  5. Deactivate Fast Boot
  6. Save the BIOS settings and exit
  7. Try to boot Windows 10 now

17. Enable Legacy BIOS boot

In some cases, switching from UEFI to Legacy BIOS mode helps fix BSOD errors:

  1. Go to Troubleshoot > Advanced Options > UEFI Firmware Settings
  2. Click Restart
  3. Find and access the Boot area of BIOS
  4. Select UEFI/BIOS Boot Mode and press Enter
  5. Enable Legacy BIOS Boot ModeWindows shows UEFI Legacy BIOS Boot mode
  6. Save the current configuration and exit

18. Inspect Event Viewer

If you can’t identify the exact problem that’s causing the 0xc000021a error, you can consult the Windows 10 internal logging utility called Event Viewer:

  1. Right after a system crash, start Windows 10 in Safe Mode
  2. Click the Start button, search for Event Viewer, and open this appWindows 10 shows how to open the Event Viewer app
  3. Select Windows Logs > System on the left part of the window
  4. Choose the first entry that says Error
  5. Inspect the General and Details tab for more informationWindows shows how to inspect a system error in Event Viewer

You can use this information to perform an online search and discover more workarounds for your specific problem. If you think that Event Viewer is difficult to use, we suggest checking out BlueScreenView. It’s a third-party app that doesn’t need installation and gives you the possibility to examine minidump files left behind by BSOD errors in a user-friendly interface.

19. Roll back Windows 10

You can roll back Windows 10 to a restore point that was recorded on your PC before you started experiencing error code 0xc000021a. However, this means losing all applications installed after the restore point was created. Here’s how to make it happen:

  1. In Advanced Startup, select Troubleshoot > Advanced Options > System Restore
  2. Select a restore point or click Show more restore points to view older restore points. You can also click Scan for affected programs to see which applications will be lost
  3. Click Next and follow the remaining instructions. Your PC will restart to complete the operation

20. Run a malware scan

A likely scenario is that a malware agent infected your computer and damaged the Winlogon.exe and Csrss.exe, leading to error 0xc000021a. Since you can’t boot Windows to run a full scan, you can use a third-party solution like Kaspersky Free Rescue Disk to create an emergency disk that will scan your PC for malware before boot. You need a USB flash drive and a second, working PC:

  1. Connect a USB flash drive into the working PC
  2. Download Kaspersky Free Rescue Disk from the official website
  3. Burn the downloaded ISO image to a USB flash drive, CD or DVD
  4. Unplug the pen drive and attach it to the malfunctioning PC
  5. Before Windows boots, quickly press the key displayed on the screen to access the BIOS boot menu
  6. Boot your computer from the pen drive or disc
  7. Update the antivirus database
  8. Run a system scan using Kaspersky Free Rescue Disk
  9. Follow the instructions to remove any infected files

21. Check the system memory

Any problems with the computer’s RAM can affect the entire operating system and cause functionality issues that lead to BSOD error code 0xc000021a. However, you can check the system memory without having to install third-party software applications, thanks to the internal utility named Windows Memory Diagnostic.

How to use Windows Memory Diagnostic:

  1. In the Advanced Startup menu, go to Troubleshoot > Advanced options > Command Prompt
  2. Select your admin account and input your password
  3. Run mdsched.exe to open the Windows Memory Diagnostic app
  4. Click Restart now and check for problems

Before Windows boot, Windows Memory Diagnostic will run a standard test to evaluate the system memory. However, we suggest performing an extended text since it shows more relevant information. Press F1 to visit the options area, select Extended, and press F10 to confirm.

You might have to remove and reset the RAM card and then perform a new test using this tool. However, if the memory card is malfunctioning, you must replace it with a new one. For example, if you’re a hardcore gamer, check out the best RAM cards for gaming.

22. Run System Image Recovery

If you have created a system backup at some point on your computer, you can use System Image Recovery to restore the backup and regain the functionality of your operating system. Here’s what you need to do:

  1. Interrupt the Windows startup sequence three times in a row to reach the troubleshoot menu
  2. Select Troubleshoot > Advanced Options > System Image Recovery
  3. Follow the on-screen steps

Keep in mind that you can’t use the system image created by another computer to restore the backup on your malfunctioning PC.

23. Use a Linux live distro

If you can’t get rid of Windows error code 0xc000021a no matter what you try, you should prepare your PC for a reset. Before doing that, though, you can create and use a Linux live distro to access your hard disk files and create backups.

You just need a tool that creates bootable USB drives, like Rufus, a user-friendly Linux distro like Ubuntu, and a working PC for creating the live disk. Here are the complete steps:

How to create an Ubuntu live disk with Rufus:

  1. Connect a USB flash drive to the working PC and make sure to copy any important files since the disk will be formatted
  2. Download Ubuntu from the official website
  3. Download Rufus from the official website
  4. Install and run Rufus
  5. Select the USB drive letter
  6. At Boot section, choose Disk or ISO image
  7. Click SELECT and add the Ubuntu ISO file
  8. Set Partition scheme to MBR
  9. At File system, select FAT32
  10. Click STARTRufus shows how to create a bootable USB drive with Ubuntu

How to boot Ubuntu from the USB flash drive:

  1. Unplug the flash drive from the working PC and attach it to the malfunctioning computer
  2. Turn on the malfunctioning PC and, before Windows boot, quickly press the key shown on the screen for accessing the boot sequence menu (e.g. F12)
  3. Choose the USB flash drive and press Enter to boot Ubuntu
  4. Once Ubuntu boots, copy all important files from your hard drive and write down all serial numbers from your licensed software applications

24. Reset Windows 10

Once you have successfully backed up your files and application keys using a Linux live distro like Ubuntu, you can focus on repairing your operating system. And the easiest way to do this is by resetting Windows 10 to factory mode. You don’t need a Windows 10 installation media disk for this solution. However, all applications and files will be deleted.

  1. Turn on your PC
  2. Interrupt the PC boot three times in a row to boot to the troubleshoot menu
  3. Select Troubleshoot > Advanced options > Reset this PC
  4. Click Remove everything and follow the remaining instructions
  5. After Windows reset, you must configure the initial computer setup

Windows stop code 0xc000021a can be fixed

To review, 0xc000021a is a Blue Screen of Death error that usually occurs when the Winlogon.exe and Csrss.exe processes stop working properly. There are multiple approaches to fixing this problem at both software and hardware level.

For instance, you can start Windows 10 in Safe Mode with or without networking features, perform a clean system boot, run Startup Repair, disable Driver Signature Enforcement, fix hard drive corruption and damaged system files, update old drivers or roll back unsupported ones, repair the system registry and BCD, as well as uninstall third-party apps or system updates.

It’s also a good idea to unplug external devices with compatibility problems, reset and update BIOS, disable Fast Boot, enable Legacy BIOS boot, consult Event Viewer for more details about the BSOD error, roll back Windows 10 to a stable restore point, check your computer for malware before boot, verify the system memory, and restore a system backup using System Image Recovery.

However, if all solutions fail, it’s time to reset Windows 10 to factory mode by deleting all applications and personal files. Before doing so, however, you can create and use a disk with a Linux live distro (like Ubuntu) to access your hard drive and back up important files and application serial numbers.

How did you manage to get rid of the 0xc000021a stop code? Tell us all about it in the comments below.

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