IMO swapping your hard drive isn't going to pinpoint anything. You'll be switching OS's and all. If you are still seeing your task manager process running at 80% then stop that process in your task manager. It will shut itself after warning you about instability etc... That should tell you if it's software related. If there are any other processes using up a lot of resources stop them too. It's the first step to finding out what's causing the problem. The only thing in my process list that takes anything over about 5% at idle is the system idle process.
