My Yosemite just greyed out my volume slider, volume keyboard keys don't work either. When I go to system preferences and click on sounds, it just froze system preferences. I tried earphones and other things, no avail. If I fire up Skype and go to Audio and Video settings, it does not output sound does not record sound and even says no camera. Anyone has this problem? Because I couldn't find any one reporting this on the internet.