Have you tried running chkdsk /r on the system?
Start/Run...type chkdsk / (with space between the k and /), hit OK or Enter. When black screen appears, answer Y and hit OK or Enter. Reboot and chkdsk /r command will run. System will reboot when command has completed.
Not sure it will help, but it won't hurt.
If that doesn't solve it, I would try either running sfc /scannow or a repair install of XP.
How To Use Sfc.exe To Repair System Files - http://www.bleepingcomputer.com/forums/t/43051/how-to-use-sfcexe-to-repair-system-files/
Many users seem to think that removing infected items eliminates the problem. I guess that I think of it as someone sticking a knife or other intrusive object in my body...removing it is a minor part of what may need to transpire before I regain my health.