If certain keys or values in the registry key HKLM\System\CurrentControlSet are deleted or given incorrect values, the registry may need to be restored before you can continue using the computer.
|To restore the registry|
Print these instructions. (If you are reading these instruction in Windows Help and Support, click the print icon.) They will not be available after you shut down your computer in step 3.
Open Registry Editor.
Click Start, point to the right-pointing arrow icon, and then click Shut Down.
Start the computer. When you see the message Please select the operating system to start, press F8.
Use the arrow keys to highlight Last Known Good Configuration and then press ENTER. NUM LOCK must be off before the arrow keys on the numeric keypad will function.
Use the arrow keys to highlight an operating system, and then press ENTER.