Reinstalling is probly the best idea.
If that works you should consider Norton Ghost. Basically you would reinstall all your apps, get your machine setup perfect then take a snapshot of the harddrive with ghost. Then if you have problems you can just blow away the drive and Ghost will put the drive back to the way it was when you Ghost it the first time.
I always do these tweaks from the audio recording world too for better performance when I first install.
http://www.pcmus.com/TweakXP.htm
I dont bother with Enable APM or Disable Write behind Caching, not sure why though.
If its still a hardware issue you really should consider trying to build your own system.You will laugh at how easy it is when your done, its only scary the first time
