Run scandisk several times first then defrag RUN SCANDISK BEFORE DEFRAGGING OR IT WON"T SOLVE THE PROPLEM.
If that doesn't work you might have spyware Spybot is a free spyware remover download it. Use it
If that doesn't work then you might have a registry problem that will cost money I recomend defender 5in1 to fix it.
If none of that works check your RAM your need a 1gig for XP to work right.
If that doesn't work buy a new computer.
OH I forgot check hardisk space. Which Defrag won't work anyway if you don't have enough. Which could also be the problem.