Addendum to my last post: Now I notice that sometimes when I open Windows Volume Control - apparently at random - the BB slider is all the way down to zero - but when I raise it back way up, I still don't hear anything. Also, sometimes the BB slider is black until I click on it.
I wonder if the Volume Control panel is accurate when it shows the volume at zero. I wonder if for some reason BB is simply not responding when I pull the slider up. In other words, it appears BB is muted, despite what the Windows Volume Control panel shows. (None of the instruments are set on mute or solo, though, and I can see them playing on the screen when I hit play.)
(See above post for all the things I checked to try to get sound)