This happened today when at work I plugged in an external speakers jack, speakers were playing, everything was OK. But after I took the jack off, I couldn't hear any sound from the Mac speakers. It seems like disabled. So now I only can listen music through headphones or external speakers but not Mac speakers.
Here are a few screenshots:
Headphones jack in:
Top Menu Icon:
When I press the increase sound button on the keyboard:
Sound Settings:
Headphones jack out:
Top Menu Icon:
(image not available anymore)
When I press the increase sound button on the keyboard:
Sound Settings:
If you had a similar situation or you know how to solve this, please do not hesitate and help me ;)
BTW, I've tried to repair permissions and restart the Mac (a few times), this didn't help.