Sound turned off, cannot turn back on

My cat stepped on the keyboard , the sound turned off, and now I cannot turn it back on. I’m running Xfce on a Xeon HP workstation with the on-board sound hardware (simple stereo). I can turn the sound off and on using either the sound control keys or the task bar mouse control. When I turn the sound off the x appears next to the speaker icon, and the x disappears when turned on. The sound level is 100%. The volume control app shows both channels are turned on.

I’ve logged off and on, rebooted, and the problem did not go away. It does not seem likely that hardware failed at the same time the cat was on the keys. How do I restore normal operation?

When you play audio is the volume indicator bar active under the Playback tab of the pauvcontrol?

What application/s are you playing sound with?