Mic isn't working

I've had my macbook since June and it has been working great, but recently the mic stopped working, both the built in mic and the line in port. When you try to record a video with the iSight all you hear is white noise, same thing if you try to plug in microphone. It started happening after me and my friend were recording something in garageband and we had his guitar hooked up to the line-in port. Is it possible that something might've jammed in the linein port? What should I do?