A continuance of my original query, which has been closed...
http://www.malwarebytes.org/forums/index.php?showtopic=26229
As directed, I did post to the HijackThis sub-forum, but since I really had no results to post, I figured I'd better post here as well....
I downloaded HijackThis, and it opened and I clicked on Do a system scan and save a logfile. However, after the scan was done and the logfile displayed for a split second..... it disappeared. I could find no trace of it on the PC. So I clicked on the HijachThis icon, and got the same message as before when I tried to run Malwarebytes - "Windows cannot access the specified device, path or file. You may not have the appropriate permissions....."
I dutifully deleted and reinstalled HijackThis only to have the exact same results. Obviously I cannot post a HijackThis log.
What now?