Sound: Why isn't any sound coming out?

Problem

The laptop, CD player or MP3 player is playing, but no sound is coming out of the speakers.

Solution

1. Check that all components of the sound system are turned on, and the amps are turned up (refer to "How to... Turn the sound system on or off").
2. Check that the left and right main faders (labelled L and R) and your input fader are up.
3. Check that the "mute" button is not pressed. An indicator LED will show next to the button if the channel is muted.
4. On a laptop or MP3 player, make sure the volume is turned up.
5. Check the connections between the laptop, MP3 player or CD player.