Why is my computer not playing audio from a video?

Things to check:

1. Make sure the volume is turned up on the computer and on the video itself.
2. Check the audio device settings in the sound menu. Make sure the correct device is selected.
3. Check to see if any audio cables are plugged into the wrong ports on the computer or video player.
4. Verify that the audio card is compatible and not broken.
5. Wipe the dust out of the audio card if necessary.