Serious computer lag problem.....?

I would go ahead and reinstall windwos XP. Depending on how old your computer is it slows down over time. I usally intsall windows every 1-2 years. You probably just need a clean install. My old PC was a Pentium III 933MHZ 512MB RAM 20GB Hard drive and it didnt have a clean install of windows in like 5 years so it was really slow and there was no viruses on it. I reinstalled windows and made it 16 times faster. If u do make sure u back-up all ur data.