Well after doing a quick google search it seems that you are not the only one with a similar problem. Others have reported the same issue after they ran spyware removal tools and virus checkers. In any case here's what you can do:
Using the windows XP cd, boot off the cd and do a REPAIR installation (will be an option after all the drivers are loaded). Let it run its course with the repair and hopefully that will fix your problem. Doing a repair WILL NOT make you lose any documents or files that you have created. It simply re-install's window's system files.