When playing video and audio files, or on Youtube, there is not sound output.
Try with installing the sound card driver:
If already installed, then Reinstall the driver package:
The problem was causes by the Volume Control configuration. The wrong audio profile was selected.
In the System settings sound pane, on the output tab, I have multiple outputs. (Digital, and analogue and Headphones).
I had the wrong one selected, and changed it so it now works.