DIRECTIONS:
1. Go To System Preference > Sound > Output
2. Keep this window open as you test
Mine was stuck on digital mode and when I plugged my headphones in, it displayed:
Name: Headphones
Type: Headphone Port
3. Unplug the headphone and watch it change name and type back to digital
4. Continue to do this while observing what mode it is in based on the name and type displayed. It should change as you continue to plug and unplug.
5. It is back to normal when you see:
Name: Internal Speakers
Type: Built-in
It may take many iterations until the audio port is finally "unstuck". I think maybe some had given up too early as I too had given up after 10 iterations. After trying again for much longer iterations, it finally worked. Remember, observe the Sound Output setting as you are doing this. Good luck!