I wrote the previous after having seemingly gotten the new machine working properly, and then I did work. At the end of the day, I went to do a little picture work on it. I'd moved it out of the lab because Mike was setting up some work machines and needed the bench space. I got it hooked up with a different monitor, keyboard, etc., plugged it in, and... the mouse was dead. A dozen or so reboots, greatly increased blood pressure, and an up to that point tolerable day shot to hell later, I can't find anything wrong or any rearrangement that will get it to come up working twice in a row.
At that point I was due at my mom's for dinner and a bridge game, and I just got back to a computer now. But I'm still closer to reaching for a large blunt instrument and going on a smashing rampage than I think I've ever been.