This article discusses the PX21, but the same steps apply for the P11, Kilo/PX11, and Foxtrot.
To use your PX21 on a PC, you must connect BOTH the headset's green 3.5 mm plug and its USB plug to your PC, then properly set your Playback and Recording devices in Windows.
1) Connect the green 3.5 mm plug to your PC's green Line Out jack (or headphones jack).
2) Connect the headset's USB plug to an open USB port on your PC.
3) In Windows 7, go to Start > Control Panel > Hardware & Sound > Sound > Playback tab.
(In older versions of Windows: Start > Control Panel > Sounds > "Playback" tab.)
Right-click "Stereo Speakers" (or something similar) and choose "Set as Default Device". NOTE: Here, make sure your default Playback device is NOT set to "Turtle Beach PX21 Headset" ("Turtle Beach USB Headset"). If your default Playback device is set to "Turtle Beach PX21 Headset", then the Chat dial will control everything and the Game dial will control nothing.
4) Next, click the Recording tab. Right-click Turtle Beach PX21 Headset and select "Set as Default Device". Right-click Turtle Beach PX21 Headset again and select "Set as Default Communication Device".
5) If you use a chat program such as Skype, Ventrilo, TeamSpeak, etc., in your chat program, set Turtle Beach PX21 Headset as both the input and output device there.
If your headset's Game Volume control still does not work, or if you do not hear any game audio, then you will want to contact support.