The sound card concerned appears to be unstable. At certain times it works and some it does not. Restarting the operating system or run the command
sudo alsa force-reload helps returning sound. This bug for this audio card is inconvenient this earlier versions of Ubuntu. I'm using Ubuntu 12.04.
What to do? I'd appreciate help on this.
Audio device: VIA Technologies, Inc. VT8237A/VT8251 HDA Controller (rev 10)