Check that the "Mute All" button isn't checked in the Master Volume Control.
The Volume Control is down the bottom of my screen in the Tool Bar to the Right, near where the time is. It's a round symbol that looks like a speaker or megaphone I suppose. (hard to tell with my eyes LOL). Just click on that and open it and it'll bring up the Control panel. Check that none of the boxes are checked for Mute.