have u connected it to your sound card .... on mine there is an output on the side of the monitor for a 3.5mm jack (plug connector thingy) then this is connected to my soundcard with a 3.5mm to 3.5mm lead
Exactly what n8 said. My old Compaq P166 (heh) came with a 15" with a built-in mic. I needed a microphone wire, but it had jacks on both ends. There was a mic jack on the top-back of the monitor, and the other end went to the sound card.