Computer problem

A wise man once told me one way to make your computer run faster was to defrag it once in a while. My poor lovely computer has been getting slower and slower, so before going to bed last night, Mike set it to work. It supposedly defragged away overnight, and I checked it just before leaving for work to see how it was coming along - not even up to 1% completed! What the hell?? What's wrong with the stupid thing? (LOVELY stupid thing...)