Okay,
what you could do is to remove the hard drive, hook it up as a slave to another computer and then after you reboot the other computer, you can run a scan disk on whatever drive letter that hard drive gets assigned.
You may be able to do other things to it as well, like possibly EXPLORE the registry and check on that setting.
You can scan the drive also.
One last thought, have you tried re-installing XP on the problem machine?
By this I mean insert insall disk into optical drive and let the software bootup as if it is going to install a fresh copy. You will need to hit the F8.
Instead of installing a fresh copy, it will detect the XP already on the drive and you can repair the existing XP installation while losing NONE of your other software. THAt will correct this problem as well.
micro...