The other day my sound stopped working on Ubuntu 18.04 desktop. I have no clue why. The sound stopped working overnight for some reason. After some research and taking a walk around Brooklyn, I found the below command to restart the sound service on Ubuntu:
pulseaudio -k && sudo alsa force-reload
All works now! Give it a try and let me know if it works for you. Follow me on Twitter @itprohelper and also check out my coffee mugs and T-Shirts shop where I design cool stuff.