Tom called the radio show and said he cannot defragment his hard drive. Based on my experiences, this may be a symptom of other issues…
My first suggestion is to check the hard disk for errors:
Check for Disk Errors in Windows XP
How to perform disk error checking in Windows XP
Check your hard disk for errors Windows Vista
Then attempt to defragment the hard drive:
How To Analyze and Defragment a Disk in Windows XP
How to Defragment Your Disk Drive Volumes in Windows XP
Features of the Windows Vista hard disk defragmentation utility
You can consider defragmenting while in Safe mode:
A description of the Safe Mode Boot options in Windows XP
Start your computer in safe mode