Mic works fine - installed yahoo messenger to live chat with friend - Mic doesn't work?

[Bobby]

So I'm what some might call an advanced computer user ( AKA Nerd) but this has me stumped. With my current setup I've used ventrilo and teamspeak regularly for over a year, just tonight i installed yahoo messenger and entered a live cam chat with my friend. Me an him talk for about an hour, then to fix him having a lil trouble hearing me clearly i decide to run the audio and camera setup thing in the preferences on messenger. We continue talking for awhile, him being able to hear me better and then suddenly he cant hear me at all. After about an hour of testing and investigating and googling my fingers off. I have determined that my speakers are now acting as a microphone AND speakers and my mic still works, but only when turned to absolute maximum in every way. I tested this by having my friend talk when i had NO MIC OR HEADSET attached with my regular surround sound plugged in, he spoke, head himself echo back in a very low quality staticy way. Any other details can be offered, but my question is basicly, how do i un-f*ck this? Is it a driver issue? Does yahoo messenger install drivers without asking when you do the setup? Any ideas are appreciated, but please assume ive tried the standard trouble shooting methods. (Ie tried another mic, tried my headset on another comp, etc etc)