Just before I left to go see the play, my computer said Time Machine had reconfigured itself and would be starting a big back-up and getting rid of the older ones. When I left it was still "preparing" and it's still doing whatever. It said it could take hours. And when I got home from the play after getting some snacks at Gelson's, it was clear that the computer had shut down and restarted. And then a pop-up saying there'd been a problem and that it had shut down and restarted.