Can't hear voice from my Macbook

Question

Well, first, I can't hear sound from my Output (only from headphones), I already tried to insert the headphone 20 times, reboot, reboot audio files, put something into the headphone plug. Nothing worked
And now, even on my headphone, audio is not coming right. I CAN'T HEAR VOICES!
On a music for exemple, I can hear all the Instrumental, but not the Vocal =O
Someone knows how to make it work right?

Answer 1

If a restart doesn't work...
Try using one of the following methods:
Restart the computer and after the chime press and hold down the left mouse button until the disc ejects.
If none of the above work, then launch terminal (in your Utilities folder, /Applications/Utilities) and type (or paste):/usr/bin/drutil eject
IF 2 DOESN'T WORK, boot into Single-user Mode and type the same command as used above. Then, type/pasterestart
     in the prompt.
Note: Only use Terminal or Single-user Mode if absolutely required. Try all other options first. If you have to use either one, be extremely careful.