I have had 3 operating systems(Ubuntu, Win7, Win8) on my computer and I have reformatted the drive for every new install. Sometimes all of a sudden my computer is really slow(I can barely minimize a window). When I check the task manager I see that there is no difference process wise (cpu usage %, mem usage) compared to when it's working normally. I really have no idea what to do in this situation, because it doesn't make any sense to me. How would I be able to diagnose what is wrong with my computer?