Audio Problems. PLEASE HELP!!!

The alerts for my Yahoo Messenger, such as mail notifications, can't be heard at all for some reason, yet my music on iTunes is able to be heard perfectly. Nothing is wrong with the speakers, and they're plugged in perfectly, by the way.

Also, some of my movie files are playing but the same problem. No audio is coming out. The same goes for streaming videos online like stuff at YouTube.com. Does anyone know what the problem may be, and any solutions, as well?

Go to Audio & Midi Setup (Applications->Utilities) and check to see if both the default output and the system output are set to the correct output.

I'm having the same problem. YouTube, Myspace, Purevolume not giving me sound while iTunes and OSX alerts and such are working normally. I checked the settings in audio like you suggested but everything looks all right although I don't really know what to be looking for.

Ditto, everything looks fine.

Hey, I actually found out the fix for this a little while ago somewhere else. It's a weird fix but it worked for me. Open up Garage band and view the keyboard controller. Play a note or two on it and then try the sounds out again. They should be working now. Let me know.