[Faith65]

From above-

To mute your microphone through settings on a Windows computer:

Right-click on the Start button and click Settings.
Click System, then Sound.
Under Input, your should see your microphone listed. Click Device properties.
Here you have two options. Either drop the volume of your microphone to zero or click on the Disable button.

Just remember to enable it again before speaking. You can also right-click on the microphone icon in the taskbar, click on Open Volume Mixer and mute the microphone.

[MayflowerMadam]

I don’t get “Settings” when I right-click on the Start button. Maybe ‘cause it’s Windows 7... ? I dunno.