How to enable Vista/2008/Seven stereo mixer

Right-click on your windows sound icon in tray, select Recording devices.

Right-click in devices list, set up checkbox at Show disabled devices.

Right-click Stereo mixer (now it's visible), Properties, at the bottom of window select Use this device (turn on), Ok.

Click Stereo mixer, then click Set default, then click Ok.

Now REC button working properly.