sound doesn't work in macbook pro I have a macbook pro and yesterday the sound just stopped working.I was funny cause I turn it off and tried and cool it down cause I thought that it's been so hot. after that it worked but after a few minutes it just stopped working.

Now there is no start up sound. there is no input and output device in system preferences.and No, there is not any red light. I also tried command option R P.

I don't know what to do. help me guys.
I had the same issue several months ago. After many hours of unsuccessful troubleshooting, I brought it to genius bar at apple store and was told to reinstall system software. It solved the problem!