Radio not producing sound.

I have an Alpine deck, and I have had it for about 4 years now, and it has always worked perfectly.  Yesterday I got in my car, and the radio would not produce any sound.  However, the deck looks as though it is working fine.  The lights all come on, it beeps when I press the buttons, and the volume knob indicates the volume going up, but there is no sound coming out.  Could this be a fuse? or what should I try doing to fix this? I really have no clue how to fix stuff like this, but I don't have any money to take it to a shop.  Please help!

Thanks.