Hardware problem?

Had a computer that may have had a keylogger or other spyware on it. Did a fresh install of Windows 7. (HP Pavillion a1114n). Processor showed 100% utilization. Reloaded with XP w/SP3. Processor at 100%. Replaced hard drive with one from retired system. Reinstalled XP w/SP3. Processor 100%. Looked deeper and in task manager, with option for all processes to show, and running processes only total up to 10%. Idle shows between 90 and 100%. But processor utilization shows 100% and computer runs very slow. This was the same behavior in Windows 7 as well. I have never had processor not total properly... I am at a loss. Any ideas?

I have looked. When I do, and nothing else is running, system idle is generally around 90-100%, as it should be, but so is the procesor utilization (number in bar at bottom, as well as graph of processor). If I launch something, system idle drops and the process may jump to 50% or so, and idle drops to between 40 and 50%. Processor stays between 90 and 100% usually closer to 100%.

To say this a different way, with processes from all users selected and showing, the numbers, without system idle add up to around 0-10%, but the processor still shows 100% on both the summary bar and the processor graph.