Long shot - but check the on/off switch !!
You won't be the first avant owner to find "someone" has turned off the avant using the very discrete button - in fact, many people don't even know its there, despite owning the avant for years,
Depending on your Avant, it may be at the back, down near the mains socket, or in a recess under the screen at the front.
This may sound odd, but it isn't that rare for seemingly dead Avants to simply be turned off by accident. Caused by kids, cleaners, etc etc.
Failing that - call an engineer.
Bang & Olufsen of King Street - Manchester,UK. SKYPE - beokingstreet