Yesterday I noticed that Task Manager was reporting my CPU was running at a constant 40% but when I checked the processes, the system was idle, running at about 3%. I thought I may have got a virus that was running a hidden process. So I scanned my system and didn't find any problem. And I did the "HijackThis" routine over on BleepingComputer.com but didn't find anything.
I was feeling like .... and

Then after a bunch of internet research, I found a program called Process Explorer from a Microsoft site (http://www.sysinternals.com/) that shows all the processes (something that TaskManager fails to do) and this revealed that the high CPU usage was caused by Hardware Interrupts. I then opened Device Manager and went one by one disabling the devices until I found a USB port that had gone bad. When I disable it, the CPU dropped back to normal.

And that's what I did with the first half of my day. But at least it worked! It's hard to do much with a machine that spends 40% of its time responding to Hardware Interrupts.

Now I feel like ...

Richard