1) Check that your headset is firmly plugged into your computer
2) Open the Settings app and go to Sound
3) Select the Recording tab and make sure that your headset microphone is enabled.
4) If your headset microphone isn’t listed, select the Properties link in the bottom right corner, and then select the Use this device check box.
5) In the same Properties window, select the Levels tab and click the Mute button.
6) Finally, try rebooting your computer.