Do the defrag AFTER doing a surface scan of the disk...the defraggers usually quit working when bad segments are encountered and sounds like your hard drive may be headed south. If it survives the surface scan, defrag then may work.
Might be better to do it in a DOS environment to preclude anything in Windows to interfere with it. Running it in Safe Mode would be comparable (if you're not comfortable with DOS), as Windows only loads minimal drivers and would be less subject to interference from something else running.
Do any backing up you can and prepare for the worst.
The surface scan should be run to automatically repair or mark as bad sectors unusable. Once bad sectors show up, their number seems to increase. Just my experience.