I never did find anything really useful on the internet, so on Chris‘ suggestion, (and after a couple of tries) I booted into Safe Mode. I then poked around under System Tools an played with a few of the things I found there. Then I clicked on “System Restore.”

I didn’t know much about System Restore, but the idea of reverting my system back to some Microsoft-backup configuration of a previous date kind of made me nervous. But, not having anything to lose, I went ahead and tried it – and it really worked perfectly.

There was a backup date just two days before the day I think the system went down, and after Restore did its thing for a few minutes, the computer started up normally. How nice – and how unusual, for such a dramatic computer issue to essentially fix itself.

Oh, the relief.