USB/Line in headset mic not picking up audio. Need Help.?

I have just purchased 2 new USB/Line In gaming headsets/mics. One for a computer at one house, and the other headset for the computer at my other house. The headset (exact same model) works in my other computer at my other house just fine, but in the computer at the house I'm at now, the headset will play sound but the mic does not pick up audio. Please help, thx.