No audio after Snow Leopard

Hi there. I've seen similar posts regarding this, but I didn't think they answered my specific problem. I recently upgraded to 10.6.1 and find that I no longer can hear other people when they are talking. They can hear me though. My sound output settings are correct in both Prefences (System, and iChat). I don't have MobileMe, which some have found was the cause of their problem. The problem happens no matter if I'm using the built in speakers, or using line-out speakers/headphones.