Macbook Pro
Problem: No sound was coming from the internal speakers.
Solution:
1. Tried resetting the PRAM (Holding Cmd, Optn, P, R at startup), no change.
2. Tried resetting SMC (Removing the battery and power, hold on button for 5 sec, replace power and battery), no change.
3. Plugged in headphones. Sound came through the headphones but when I removed them, still no sound. However there was a red light on in the headphone socket. Apparently this is the optical out socket also and the light on meant that the optical links was active.
Finally I used a toothpick and ran it around in side the socket (with the computer off) restarted and had sound, and no red light.
