I can't hear my iChat sounds?

Incoming message, outgoing message, buddy sign on, none of those work. Also in System Preferences/Sound when I click on a different alert sounds they don’t work. I just tried it again and the screen flashed (same as in Photobooth) each time I clicked the different alerts. Weird! Now it isn’t doing it anymore because I unchecked Play User Interface sounds. Now I checked it, and they still don’t work. In iChat when I select a sound to play, it works. But after I exit the preferences they don’t work anymore. Now that I think about it, my alerts haven’t been working for a while! I had Submarine set and it would always play when I deleted iTunes songs but it hasn’t been doing it for a while!