You may need to set the default recording device and if you have "System Mixer" (may be called Stereo Mix) you should set that as the default recording device.
Go to the Control Panel/Hardware and Sound and finally the Sound Panel. In the Recording Tab section it will display the recording device options. If the System Mixer/Stereo Mix is shown, make that the default recording device. If its not shown, RIGHT click in a blank space in that panel and then check the boxes to show disabled and disconnected devices. If it now shows up you can enable it and then make it the default recording device.
This usually takes care of the problem, if you are using the PC's sound device.