I have been unable to defragment the C drive on my computer. When attempting the defragmentation procedure, the error DEFRAG004 appears. This same error also occurs when running Disk Defragmenter in Safe Mode. The computer is running Windows 98.

This error message generally indicates there are errors on the hard drive, and Disk Defragmenter is unable to complete operations. In this case, you should try running Scan Disk to detect and fix any identified problems. Boot the computer into Safe Mode, and then open Scan Disk. You can access Scan Disk by going to the ‘Start’ menu > ‘Programs’ > ‘Accessories’ > ‘System Tools’ > ‘ScanDisk’. In the window that appears, enable ‘Thorough’ and click ‘Start’. This process will take a while to complete, and you should not do anything on the computer until it has finished. Once Scan Disk has completed, restart the computer back into Safe Mode again and then try running Disk Defragmenter. Hopefully, the Disk Defragmenter should run properly.