sound on macbook pro not working

[Adelaidie]

I just got a new mac about a week ago and the sound has already gone out. I didn't do anything weird, that I can think of, it's just not outputting sound. whenever i press the f11 and f12 buttons to adjust the volume, a circle with a line through it appears. In my system preferences i put that i wanted volume to show up on my menu bar, and a space appeared, but there was nothing there. when i turn my computer on, the sound that it makes turning on sounds, but no other sound comes out once the computer is actually on. I've been looking at other forums and people with similar problems as me have been putting headphones into the jack, but there is no red light for me, so i don't think that will (and it hasn't yet) fix it.
Lastly, on my itunes, whenever i play a song, it comes up as now playing, but it just stays at 0:00. and obviously, no sound comes out. does anyone know what's wrong and how i can fix it??

[Adelaidie]

also, when i go to sound preferences and hit "sound effects" the mute box for the output volume is already checked and it won't let me adjust it or change it. it's grayed out...and i can't click on it.

[meagopi]

sound is not working what i must to do