|Please try System Restore from safe mode command prompt before entering the OS.|
Restart your PC and press F8 key just after BIOS post screen.
When you are at the command prompt, give the command
If C:\Windows is different in your PC, change it accordingly.
I remember, rstrui.exe was in System32 directory. Please check it.
If still no joy, use a virus scanner from Command Prompt.
Also see http://support.microsoft.com/kb/950505 before doing anything.
Hope the above helps.