It is important that you connect the VCR/camcorder output sound directly to the line-in of your computer soundcard.
Or if you are capturing a TV show directly from your TV tuner, please make sure that the sound output of the TV tuner is connected to the line in of your sound card.
If the TV tuner doesn't have a sound output port, then the sound output must be internal. It should most likely be connected to the CD in port of your motherboard. If this is the case, set the input audio to come from the "CD Audio". Then make sure that your sound card settings are setup to get audio from the line-in where you connected the audio input. Go to Control Panel and open the software for your sound device and set it up properly. Contact your sound card manufacturer for help in this area.