I just installed Ubuntu 16.04 on a new computer. The sound worked fine for all users right after the installation but suddenly, the sound indicator was set to mute and I was unable to adjust the sound (the sound still plays though!!).
If I login as a different user (or even to guest session), the sound and sound indicator both work flawlessly. I tried to reinstall ALSA and pulseaudio but nothing changed. The weirdest part is that sound comes out of the speakers.
I don't think its a hardware detection failure because sound is coming out of the speakers, I have no idea what to try next - thanks in advance for the advice!