As I mentioned in my original post, I was also having problems with the BIOS settings. Some were changed from what I had set them to. I have no idea how that happened.
The best I can say is "something" went wrong, but what, I don't know. In any case, I've got the BIOS settings back the way I want them, and ntune/nvmonitor works again.
XPSP2 event viewer shows no problems at the time when these problems were occuring.
However, I just noticed there is a minidump dated yesterday, but I can't read it.
-Bob