Have you ensured your audio recording settings are correct in your OS?
You can do this by right clicking the speaker icon in your taskbar and selecting recording devices. Make sure the "line in" device is set as the default recording device. If there is no "line in" device, right click in an empty part of the device menu and ensure "show disabled devices" and "show disconnected devices" are checked off. Then, if the device appears, right click it and select "enable device."
Report back your results and we shall go from there.