Yesterday while watching a video on youtube, my audio stopped working. In fact, the hardware (sound device) was no longer visible nor was the speaker icon on the menu bar.
I read through this thread (http://discussions.apple.com/thread....art=0&tstart=0), and tried the safe mode reboot. It worked. Sound came back. Watched another video and same thing happened. This time, the Safe mode reboot didnt work, but clearing the audio cache via Onyx did. Watched another video, same thing. Safe mode didnt work, Onyx didnt work, but PRAM reset did. Watched another video, same result. Now nothing works. WTF?
The thread suggests a hardware problem (ribbon cable or board itself). Seems doubtful to me since some of these workarounds actually worked.