I have a very strange issue with my microphone. I was playing around with an external USB sound card (it didn't end up working with ubuntu, but that's not what I'm asking about). When I unplugged it, the mic stopped working in exactly two applications that I'm aware of: skype and google hangouts. Bizarrely, I can still record audio in audacity, and a windows XP guest that I have running inside virtualbox can also read sound from the microphone just fine. And I should point out that the mic has worked fine for a year before this.
I opened up pavucontrol and I can see the 'internal microphone' listed. It seems to be responding correctly (I can see the volume indicator on the bottom bouncing when I make noise). However, if I go to ubuntu's settings and look under the 'input' tab of the 'sound' settings, I can see my sound card listed, but the controls (volume/mute) are grayed out, and the 'Input level' indicator does not seem to show any sound. So somehow the mic signal is being lost in between pulseaudio and unity? It's hard to believe this kind of situation is even possible.
I can open up alsamixer, but the mic control on my sound card doesn't seem to have any effect.
I'm running Ubuntu 15.04.
Output of alsa-info is here: http://pastebin.com/fFPTYV5N