Strange Ventrilo Problem

My mom decided she wanted our sound to come out of the speakers built into our monitor, when I went to make the sound go into my headset so I could talk to my friends on vent in peace, it wouldn't work. I can hear my music, the sounds it makes when you talk in it, MSN bleeps and so on, but not the voices of the people on vent. What's going on?

Can you hear the voices normally when not using the headset?

I don't totally understand, it can come out of my moniter speakers but I only did it once. I want it back in my headset.

Are your Vent settings correct? The Inbound and outbound audio should both be set to your headset.