Sound of my MacBook Pro

Everytime I start my computer the sound is set in mute as default. Do someone know how to fix it? Thanks

In System Preferences under Sound, you don't have the Mute box checked next to Output Volume, do you?
I know it sounds basic, but I always start with the obvious when trying to fix something weird like that.

The thing is that everytime I turn on my computer the mute box is checked by default even when I turn off the computer and make sure the sound is not muted.

I just check and if I plug in my headphones just after I turn on my computer the volume gets back to the one I previously had and if I take them out it goes back to mute.