Can't unmute Ubuntu Unity 22.04.2 LTS

I have a strange problem with Ubuntu Unity 22.04.2LTS on my ThinkPad T420. When I click on the sound icon on the right side of the top bar, it indicates the sound is muted. I cannot "uncheck" the box. I get sound out of VLC, Audacity and WINE applications, but I am not getting alert sounds, nor is any sound coming out of sites I visit with Firefox. The last time this happened, I used Synaptic to reinstall ALSA and rebooted and it worked again, but this time not even that worked. Oddly enough, if I boot into the "Guest" session (yes, I enabled "Guest" sessions), everything works fine... it just doesn't work when I'm logged into my own account. Thoughts?