audiomacbook pro
The sound output is not stuck in digital mode, actually the output is stuck in "headphones mode". It works when the headphones are plugged in.
Plugging in or replugging the headphones does not change mode from headphones to digital, it stays on headphones. It does not solve the problem either. There is no red light. Instead there is a white light. Blowing at it failed to work.
When you insert the headphone into the socket, it makes connections internally against a number of poles which connect to the different rings on the jack end (left audio, right, mic, ground, data etc..). These are essentially tiny spring loaded contacts which the jack must push aside when inserting, that then rely on sprung pressure to maintain a permanent connection to the ring on the jack. Here are a couple of pictures, a diagram, and a photo or a replacement part that shows one of the poles:
These poles can jam, get stuck, fail etc etc. Usually a vigorous insertion is enough to free them, but this is relying on the chamfered edge of the jack to transfer vertical motion into a horizontal movement of the pole. You could use something slimmer than your jack, and insert (carefully, ensuring you don't insert it too far) before applying sideways pressure directly to the poles to try to get more energy into making them move.
Headphones and the Internal speakers are only OR option.
You can not have AND.
If your headset sometimes does not switch, check the plug for dirt stuck in it.
If it is not the hardware, reset your SMC.
Best Answer
I had a similar problem when I used an older version of AirParrot, it would not switch the Audio back to Built-In. Had to manually go into preferences.
If you checked the System Preferences -> Sound -> Output and System Preferences -> Sound -> Sound Effects and it does not show Built-In option when headphones are out:
If still the same, I would bring it in to Apple store since they will diagnose it for free.