Ouput plays thru Mic


In Runtime
When I record/use microphone with no other sound running on my computer it works fine...but If I'm in ventrilo and I speak while someone else speaks the mic plays the sound from my headphones and transmits it to everyone in vent. When I record u can't hear my voice all you hear is the sound from the music I'm playing because it is extremely loud. How do I get the output from my headphones to stop going to my microphone and I know it's not turned up too loud, that is not the issue. Is there somethign I have to change in my settings?