No sound from mac, how to find the problem? Good day, I have Macbook Pro 2012 with el Capitan 10.11.3.

The problem - no sound from my mac.

I have listen the music, after that I decide to insert headphones, when I'm taking out the headphones sound from Mac disappeared and there is red light from audio jack. Between that I have made an update from 10.11 to 10.11.3, maybe the problem is with that?

There was not any sound from my mac on startup, but when I have use disk utility repair the sound on startup appears.. 

How can I diagnose myself where is the problem and fix it ?
Your MacBook believes you've plugged in an optical audio cable when you haven't.

Turns out, that headphone jack is actually a combo jack that has both optical audio and analog audio. There's a little lever in there that detects when you've put a cable in there that's probably stuck. Try fiddling with a toothpick or repeatedly plugging and unplugging.