MacBook Pro

I have this Mac for over one year but I never tried to use headphones to listened music until recent and the big surprise was: zero sound in my ears. After some research on the internet I find the solution: from Applications/Utilities/Audio MIDI Setup.app after you plug in the headphones you must uncheck Channel 1 and 2 from Mute column and this is all.
This was the most stupid thing what I sow on this Mac until now... and without internet help you have no chance to find this stupid setting.