Well, bumpkins, it appears I will be giving out the reward after all... to myself!!!!!
Reformatting and having it disconnected from the network did nothing. It seemed like it worked at first, but after a few days, it started up again. I eventually did track it down to the Mixer.exe which was loaded with the C-Media audio drivers. I had previously viewed that as a suspect, but thought I had eliminated it by removing it from the startup registry. Not so. Apparently it was in there twice, both before and after the format. After removing both instances, and preventing it from loading at startup, the computer runs beautifully. And you all thought I was infected.
As I had thought, it must have a memory leak or something, because it gets bloated and uses up all the resources. Take that, mixer.exe!
Reformatting and having it disconnected from the network did nothing. It seemed like it worked at first, but after a few days, it started up again. I eventually did track it down to the Mixer.exe which was loaded with the C-Media audio drivers. I had previously viewed that as a suspect, but thought I had eliminated it by removing it from the startup registry. Not so. Apparently it was in there twice, both before and after the format. After removing both instances, and preventing it from loading at startup, the computer runs beautifully. And you all thought I was infected.