Maybe it was the purposeful look in my eye and the screwdriver in my hand as I approached the tower with the intent of removing the hard drive, but I gave it one last try, and voila — the desktop is functional again!
(Perhaps I will just never turn it off again. Why it worked this time and not the countless other times I tried in the past ninety minutes, I do not know.)
Yes, I have already backed up all my work files to my Gmail account. All my important personal writing stuff is already on the thumb drive I carry in my purse, and… no, I didn’t save the latest Pandora stuff to it last month. I will remedy that immediately.
Then… to work!