So, You've downloaded a video (screencast for example) and you can't hear a thing and you're running Vista? You know that your "setup" is correct because you can play music. You know that the video contains audio because you can see the oscilloscope/spectrum analyzer jump. Yet, there's no sound. If you look at the audio codec (file -> properties), it will probably say that the audio is something "mono"... I bet you have a fancy 8 channel audio card with rear panel: front, rear, side, sub/center,...