Sorry if the last one sounded little off, didn't mean it to, it's just many were implying that the hardware was disabling itself, where it was just a case of muting.
Anyway found the fault and he's in for a slap. You were right it is an app, very obvious when you think about the issue, but not so, until you don't have all facts.
It turns out he installed a third party screen saver and guess what it does? Play music, but guess what he had done? Muted it. However it seemed to have an issue where it doesn'e unmute itself when the pc is resumed. We turned of the mute on the screen saver and guess what. It no longer mutes!
Helps when people mention these things I guess....
Thanks for the help