My Sound isn't working!

I've tried all of the sound preferences! No, mute is not checked. It won't even let me check or uncheck it. Also, when I try to turn the sound up or down it is shown as all the way up with a faded sound icon and then a little circle with a slash. I was wearing headphones earlier and it worked fine, then I was watching videos and it was fine and then it was going on and off during my video and now it won't work! I've restarted my computer several times and restarted PRAM. What is going on?!?! Please Help!!!! <<<<------ that is what the sound icon looks like in the bar (it's all faded) <<<--- this is what it looks like when I try to turn it up and down