After a clean install of Ubuntu 12.04 on my Dell Inspiron 6400n Laptop there is no sound on any application I use apart from the log in screen ready noise. If I click on the speaker icon on the top panel then sound settings it tells me that the default playback device is S/PDIF. In alsamixer the slider is set to zero. I am sure it should be HDA intel or similar. How can I get the sound working please...?