MaxxAudio and headsets

I have a headset with two pin connectors- one black and one gray. When I plug either one into the jack on the front of my Vostro 5880, MaxxAudio asks me what kind of device I have plugged in. No matter whether I choose "Headset-On Ear", "Microphone" or "Line In", neither Sound Recorder nor Audacity seem to hear anything spoken into the headset microphone. The headset works fine on my older desktop. Can anyone offer any suggestions as to what I am doing wrong?