TODO:
Have you ever unplugged your headphones, and the internal speaker does not work, and it is simply greyed out? You will also see a red light coming out of the headphone jack.
SOLUTION:
Use a toothpick and wiggle it in the headphone jack hole. You can also insert and remove the headphones a few times and the internal speaker should kick on.
NOTES:
Sees to be a sensor gets stuck that turns on the Optical Input inside the headphone jack.