This happens on occassion on the Mac Book Pro – You lose the internal speakers and are only left with digital out. A sign this has occurred is that the red light in the headphone port (where you plug in your headphones) will be on.
There are numerous ways to try to fix this, anything from system preference tweaks all the way to opening up your Mac Book.
Here’s the simplest thing you can try (and it does seem to work with a bit of persistence):
- Open System Preferences > Sound
- Plug in your headphones as you won’t have control over the volume/mute of the digital output
- Once headphones shows up on the list, move the volume slider up and down and check/uncheck the mute button.
- Unplug your headphones
- Check if digital out has disppeared and been replaced by Internal Speakers.
- Rinse and repeat. Note it can take several attempts before this works. For example, after 3 times, I finally had internal speakers appear for a second then disappear back to digital out. On the fifth attempt, internal speakers appeared again and this time stayed. Basically what you are doing is trying to get the Macbook to recheck its sensors and correctly revert to internal speakers.