Windows Update basically works in conjunction with the registry and different DLL, OCX, and AX files. In case these files go corrupt, most features of Windows 7 including Windows Update will stop working. Fix WU is a free light-weight and portable utility to fix this problem in one click.
It basically re-registers a total of 114 .dll, .ax, .ocx files required for the proper functioning of Windows Updates. Simply download and run the tool and hit the Fix Windows Updates button. It will take some time before you receive the process completed dialog box.
It works perfectly on 32-bit and 64-bit versions of Windows Vista and Windows 7. Enjoy!