General Computer/Windows problems

Hello,

I have had my Dell for a little over a year now. I am having a major problem.

My Windows XP OS is the main problem. I can't use the mouse to switch between programs in the task bar, I usually have to use the AltTab method to switch between applications. And sometimes when I bring up an application, I can't click on anything inside of it (mostly this problem is with Internet Explorer). I have reinstalled Windows several times, and this error continues through every reinstallation.

The only thing I can think it is would be a hardware issue. I had to replace the case fan about 6 months into owning it, because the computer sounded like a freight train while running. I wonder if possibly the computer has overheated due to this new fan.

Any ideas/suggestions would be greatly appreciated.

Thank you