Strangeness is happening: first, but not foremost, the Forum didn't recognize me--well, it knew my name, but it made me log in, which is not usual,
since I was up to now logged in forever. Second, but still not foremost: Right after logging in after boot, frequently but not always, I get a black
notification, "Multimedia System The audio playback device HDA Intel (ALC662 rev1 Analog) does not work. Falling back to"--but the audio works.
Now, the main thing: After some period of time--not measured, but less than about 1-1/2 hours, the screen goes black. The computer is still on, but
the monitor is black. Nothing I do at the keyboard will bring it back to life--hitting return, or escape, or Alt+prtscrn +REISB, or anything. I have to
hit the shutoff switch on the machine, then turn it back on and boot up. I have unchecked everything in Power Management, and also verified that
the settings in Screensaver are all greyed out.
The Forum problem is new today, I think. The audio complaint has been around for a week or so, and the time out to totality started yesterday.
Maybe after last system update, I'm not sure. Before that, I had the Power Management set for 15 minutes screen darken, and 30 minutes
suspend session. That worked sometimes, and sometimes not--sometimes I could go to bed and in the morning the machine would still be up and
running, monitor and all. I'm baffled, and I don't have any idea what to do next.