disk defragmentor will not defragment

Two weeks ago I ran the disk defrag. and worked fine. Had problems with isp and their tech support had me change some things in the settings. Was unable to finish what he started–some components of the windows 98 program were missing. Told to reinstall win 98 to restore those missing parts. Then he would give me the rest of the numbers. The next tech said there was nothing else he could do. Now the defragmenting will not get any further than 16% then it says that components have changed—restarting. Tried to repeat this process again and it will not get past 3% and then restarts the defragging again. Can you help?