what OS are you using, XP or Vista?
-Do you have a floppy disk drive and a floppy disk maybe in the drive, if so remove floppy
-Same thing with CD rom drive, remove CD if one happens to be in the drive
if using XP, a repair installation may be what you need to do if above do not apply
Repair Installation
A Repair Install will replace the system files with the files on the XP CD used for the Repair Install. It will leave your applications and settings intact, but Windows updates will need to be reapplied.
Perform a Repair Installation