Have you ever installed something new, or un-installed something you weren't sure of or made a drastic change to your computer or the registry.
The quickest way to fix it is to restore a previuosly saves version of the registry.
To do so you can do 1 of 2 things:
Number - 1: - Go into DOS mode with a Start-Up Disk choose option 4 (minimal boot) - at the DOS prompt type: SCANREG /RESTORE - restore to 1 or 2 days back - restart computer when prompted to
Number - 2: - goto START|PROGRAMS|ACCESSORIES|SYSTEM TOOLS|SYSTEM RESTORE - choose a restore point a day back or use one of the system checkpoints that indicate a major change to the computer - then press restore and the computer will restart
Hopefully one of these methods will help you with a problem. These methods don't always work but help most of the time.