Althougn the computer had started on Saturday afternoon without any apparent problem, and again later that day after I had downloaded and installed 3 updates indicated as urgent by Microsoft Update, it would not start on Sunday morning without resorting to options 1 & 2 mentioned above.
The most recent GoBack restore point that generates a successful Windows startup is Saturday morning. Nothing more recent will make Windows start successfully. Each time I use GoBack and return things to Saturday morning, I lose important files -- including the Outlook file. That meant that I lost several very important emails that I had sent and received on Sunday. Fortunately, GoBack has a tool that can recover files more recent than the restore point used and that saved my bacon.
I have scanned using Ad-Aware and it discovered something called "Alexa" and removed it: that didn't solve the mouse jumping problem. I have run Norton WinDoctor and it has fixed 2 categories of problems (it says): a couple of improper file extensions and a couple of ActiveX problems: that hasn't solved anything either. I have used Registry Mechanic 5.2.310 (the latest) and it claimed to fix several hundred problems -- without solving the ultimate ones.
I am now running a Norton AntiVirus scan (maybe it was silly to wait this long, but it takes several hours on my machine; I run a complete scan one night a week with up-to-date virus definitions; and I go for years -- truly -- without any infections) At this point, it has scanned about 600,000 files (out of about a million) without discovering any "threats."
I have made regular backups using BackUpMyPC. The most recent one was yesterday morning, so I could use that path to recover important data, if necessary, up to that point, but I don't think I could trust the regestry files that it backed up -- they would be the same corrupt ones that seem to be plaguing me now, wouldn't they?
Any help would be appreciated. I would be happy to provide any additional information.