Sometimes when reboot my macbook pro, I have no sound and optical turns red light on.
So I found a good advice by Michael Bransome
Then I tried this: opened Sound prefs, went to the pane for device for sound output, stuck the headphone jack in, at which the device name changed to headphone, then I clicked on the line showing headphone, but I *held the mouse button down*, and while holding it down removed the jack. This made the device name change to internal speaker, and it worked again…
I was everytime angry this save my day 🙂