Playback Meters active, actual sound suddenly gone forever

Playback Meters active, actual sound suddenly gone forever, right in the middle of an edit job.
Windows 7, Audacity 2.3.2

I’ve been using Audacity for years to edit radio audio, never ran into this before.
Especially right in the middle of a project with a deadline!
You might think the computer’s speakers, wires, etc., are at fault, but they still work fine for Winamp, VLC, WMP, etc.
You know the all-purpose drill: quit then restart Audacity; soft reboot; drastic reboot. All for naught.
I did not reinstall Audacity. None of these moves would reveal the problem’s cause.
Editing features are still OK, but I can’t hear the result without exporting it.
(My temporary solution: move the project over to a despicable W10 laptop, same Audacity version.)

Check your [u]Audacity Playback Device[/u].