This morning I had a strange problem where sound stopped working on my MacBook Pro running 10.6. The speaker icon in the menu bar was grayed out and the image brought up when pressing the volume up and down controls indicated that sound was muted. Bringing up the Sound control panel in System Preferences didn’t help.
Last night I had been listening to music on headphones using the line out jack, so I was puzzled as to what might have caused the problem. Restarting and zapping the PRAM didn’t help. Interestingly enough, though, the start up chime played at system startup. So, I knew the built-in speakers still worked. However, the login sound was muted.
When I brought up the Sound control panel, the only output device showing was digital out. The normal Internal Speakers entry was missing. So, I guessed that maybe OS X was confused about whether I was still trying to use the line out.
I started up a song in Songbird and still no sound or ability to control the volume. I then plugged in my headphones and, voila, sound worked. I unplugged the headphones, but the internal speakers didn’t take over. In the Sound control panel, Headphones appeared as the output device when I plugged in the headphones, but Digital Out reappeared when I unplugged them.
Finally, on a whim I plugged back in the headphones and clicked on the speaker icon in the menu bar that represents the volume control. While holding down the mouse button, I unplugged the headphones and suddenly the internal speakers started working on. In the Sound control panel, the Internal Speakers entry had returned. I don’t know exactly why, but that solved the problem.
Update:Problem happened again on 11/24/2010. I’m running OS X 10.6.5. Same fix worked.