Configure the microphone as your recording source.

Step 1: On your computer go to Start > Control Panel > Sounds and Audio Devices

Step 2: Click the Advanced button in the Device Volume section of the Sounds and Audio Devices control panel.

Step 3: With the Volume Control open choose Options > Properties from the menu and click the button next to recording.

Step 4: Make sure the Select box under the Microphone column is checked and the volume is above zero or you won't be recording anything.