The following is a technique you can try when stuck, but it requires some faith as you're going to be doing it silently (like there's any other choice under the circumstances you'd need to use it).
1. Hit WinKey+R
2. Type sndvol, which is going in the Open edit box without feedback, then press Enter
3. The volume mixer will have opened, and focus will be on the main speaker/headphone volume.
4. Try up arrow multiple times (at least 10 or so) until either you actually hear the Windows volume chimes getting louder with each press, or it stays silent. If you're hearing something just keep going up with the up arrow until you have the volume you want and close the volume mixer window.
5. If you hear nothing after multiple up arrow presses at step 4 that means you have actually used the mute function rather than just lowering the volume to zero. Now hit TAB, once, which should have you on the Mute/Unmute toggle button for the main speaker/headphones. Hit spacebar, this should unmute your speakers to whatever volume you had them set prior to invoking mute. However, this gives no auditory confirmation that it has worked, it just unmutes the speakers. Now SHIFT+TAB to throw focus back to the volume slider and play with up and/or down arrow until you have the volume you want.
If you play with this a few times just to get confidence with it when someone's around to bail you out, if necessary, you'll get the hang of it quickly.
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Explanations exist; they have existed for all time; there is always a well-known solution to every human problem — neat, plausible, and wrong.
~ H.L. Mencken, AKA The Sage of Baltimore