Try going to Control Panel > Sound > see if you see the GameCon 780 in there. It might be disabled. In that case just right click it and Set as Default Device.
The headset is plugged in and it is set up as default. When I go over the speaker icon I get this notification that says: "No speakers or headphones are plugged in." I then click on it again to try and troubleshoot and get the same response as what you're proposing -- that the audio device is disabled.