Or tinker with services? If so, undo both steps.
Also, try the ideas at http://www.winhelponline.com/articles/60/1/How-to-fix-Disk-Defragmenter-problems-in-Windows-XP.html
I have XP Pro, SP3.
In the built in Computer Management is a function called Disk Defragmenter. It's not showing any files when I hit Analyze or Defragment and the reports, either one, never show any fragments and report 0 files. Does anyone know what's going on and how to fix it?