Check the following:
- Make sure the A/V Mute button is not enabled.
- Use the Volume button to increase the sound.
- Make sure the sound cables are connected properly. For computer audio, the cable should be connected to the computer's headphone jack or audio out jack.
- For computer audio, make sure the volume control on your computer is not turned all the way down or muted. On a PC, you may be able to check this by clicking the volume control in your Windows System Tray (in the lower-right corner of the screen).
- If there is still no sound, try connecting the speaker to the computer or video device to make sure the sound from the device is working.