Volume control doesn't work

Let me explain the problem here, the internal speakers are not broken, they work just fine and the sound is all the way up, I can mute and unmute using the respective keyboard buttons BUT I can't lower or raise the volume, a little stop symbol like this one appears (http://staticz.com/wp-content/uploads/20...). There is no light coming from the jack port.

Note: With headphones the volume controls work.

I tried to search the problem on the internet but all the solutions i found didn't work for me.

Here is a list of the things that I've tried and didn't solve my problem:

- rebooting

- clearing cache by starting in Safe Mode and restarting

- checking System Preferences > Audio and everything is good (internal speakers are set as output)

- plugging and unplugging headphones

- using a toothpick to click the little button inside the jack

- pastening "sudo killall coreaudiod" in the terminal app

- resetting PRAM / NVRAM with cmd, option, P and R

- switching between users

Thanks in advance!