Open the volume control window from the icon in the tooltray (if it's not there even after you use the little arrow to show all icons there, you want to tick Place Icon in Taskbar in the sounds and audio bit of the control panel).

Then go to Options, Properties, and change from Playback to Recording, and depending on your soundcard, you should be able to either choose which channel to silence now for when you want to record stuff, usually everything except either Microphone or LineIn depending on which socket you plugged the mic in - or select the single channel to record from instead of silencing the others It's probably everything mute except Wave, or record from Wave only, which is causing it to record WMP instead of the mic



The computer won't detect the microphone normally, much like it never detects your speakers, only the sound card - it doesn't really care about it, and only about the sound being sent into the actual socket on the back of the PC