Look in the headphone out, do you see a red light? Try plugging and unplugging a headphone jack in and out several times. If still no joy, cut the end off a Q tip (or a wooden toothpick, nothing metal or conductive) and insert it in the headphone jack and very GENTLY "massage the jack (stop at the least resistance). There is a micro switch that switches between digital and analog output that sometimes gets hung up. Reboot. If still no joy, go to system preferences and make sure that the output tab is not set to mute. Also you can go to utilities>audio/MIDI setup and make sure it is set to built in speakers for output. Hope this helps. Last, power down, then power up holding option, command, P, R (no commas) and continue to hold these keys till you hear the start chime 2 times, then release. Reboot.