Garageband won't play audio!

Hey guys I just downloaded GarageBand on my Mac and decided to choose the Hip-Hop project just to test itout. The project gives you a small sample track. When I play it does not make a noise. To make sure it wasn't just that track I created a new one and open the keyboard window. When I click a keyboard key there would be no sound! Looking at the master and track volume slider, when you play the track the green bar won't show (the green bar showing the loudness of the track). Even the metronome won't make a noise! Please help!