[XP] Mic does not work - no sound input

I am trying to install a headset (speaker & mic) on my friend's desktop. All plugs are correctly inserted. The speaker works perfectly, but the mic does not seem to respond.

Any idea ?

Thanks

Sorry - Have to ask: Did you check the Windows volume control to make sure the mic or line in aren't mutted?

What sound card are you using? Some, such as Creative, will have a control panel utility where you can select the inputs.