sound only works through headphones?

look inside the headphone jack and see if there is a little light on, if there is a light on the sensor inside got stuck down so it still thinks there is a jack in it. if the light is off check all the sound settings in system preferences and application settings. if all those are fine call apple because it could be a bunch of different things most of them are hard ware issues (i had a similar issue on a power book because my logic board was bad supposedly, not sure if that was it or not because it took so long my machine was just replaced)

-matt

When you unplug the headphone, is there any volume bars indicated in the menu bar? Headphone volume and the w/o the headphone jack work as two different settings. If that's the case, then just turn up the volume 🙂

there is a little thing that is like the switch on your fridge (just backwards on when the light comes on)

you can try using a head phone plug in and out a few times (not suggested because it can "prematurely wear out the plug") or use a tooth pick to poke the little switch so it doesnt hang up. if it keeps happening and your machine is under warranty it should be covered under warranty if not apple can still swap it out but it may cost you.

ive never had to get it to stop catching but many people around here have had to and say a tooth pick used carefully works well

-matt

Yep, toothpick works but be gentle. Find the spot, you will hear a click, the red light will go off and your speakers will start working again.

Another Fix:

Plug in a headphone jack and close the cover until the machine goes to sleep.
While it's asleep, unplug the headphone jack.
Wake it up.
The Optical light should go out.