I have exactly this problem and here is what seems to fix it: 1. Bring up system preferences - and 'sound' settings within it. 2. connect your headphones or jack lead into the audio socket. 3. From the apple icon menu in the top left corner of the os x screen, tell your computer to go to sleep 4. Immediately wake it up again from sleep 5. A second or two after waking, under 'output'; 'internal speakers' should change to 'headphone port'. NB. Weirdly, this fix switches the output to headphone port, but you lose the option for internal speakers at the same time. However, to switch back to internal speakers, remove the headphone/jack lead, put the computer to sleep then re-wake it. This switches it back. Hope this helps! Peace ;)