have you recently installed service pack 2?

 

Get norton ghost or just use the windows backup. Put the back up on disk and format the HDD. Reinstall windows and then load what ever folders you need from the backup. Youll be done in a hour instead of messing around with trying to fix it.

 

Sounds kinda like a bug to me....

I would go out and get ad aware and run it on your system before I did the fresh reinstall.

http://www.lavasoftusa.com/software/adaware/

If this doesn't catch it, then you may end up having to reinstall. But I would try it first...