Hi, sounds maybe the sound jack didn't close properly?
Have you done a PRAM reset, CMD+Option+p+r...
In fact, do 3 in a row, takes a bit of time.
Long shot, but...
Open Audio Midi Setup in Applications>Utilities, see the input & output options & KHz setting there, some things will change it for their own use, then not set it back.
I found this thread while searching for a solution to a similar problem. Mine turned out to be that my previous LogMeIn session left the sound output on the LogMeInSoundDriver. I did not specifically set this, but it remained in effect after the session nonetheless.
- Settings -> Sound -> Output tab -> switch from LogMeInSoundDriver to Internal Speakers
Hope this helps others who may stumble upon this thread.