Internal mic not detecting audio - 2011 Macbook Pro Mavericks 10.9
This happened to me the other day. After checking all the obvious settings etc. It actually seemed as if there were either no drivers or the actual hardware had been removed, like the OS didn't acknowledge its presence at all. I spent ages trying to work it out and what got it working again was just plugging something into the 3.5mm TRRS audio input/output jack on the side.