One of the most regularly reported problems with Windows Vista is that the hibernate function, one of the power saving modes, does not work. Hibernation a feature which allows you to save the fully working desktop with all applications from your memory to your hard drive, and then power off the system, which you may power on at a later time to resume work from the point where you have left it. It is possible that you may find no hibernation option in your start menu, there can be few reasons, for example, your PC doesn’t support hibernation or you have the hybrid sleep mode turned on.
To bring back the hibernate option, follow these simple steps:
Go to Vista start search menu, type cmd, right click on it and select Run as Administrator.
Once the command prompt is launched, type in the command, powercfg /hibernate on
This should now enable the Hibernate feature under your PC.
Sometime you may need to turn off the Hybrid sleep option to allow the hibernate option to appear under start menu.
Go to your Power settings and click on Change when computer sleeps.
Now at the next window, click the option change advance power settings, It should open the settings window.
Navigate to the option Sleep, under that set the option to OFF, which says allow hybrid sleep
Apply and it should bring the hibernate option back to your start menu. This method should work with Windows 7 as well. Enjoy!