hi mate,
im going to presume that you have the full vogue spec with the preimum sound system do you have DSP on the menu screen? if you dont then it is more than likely be the main amplifier not getting power. In the rear load space their is a compartment on the left hand side, remove the panel cover and remove check the amp multiplug is connected properley. The amp is the black unit at the bottom with what looks like fins. This area is a common area for water ingress so check for water damage, if there are water stains or the connections on the multiplug are corroded then you have a water ingree problem from the window a above the compartment and you might need new units. If after check the multiplug and everything is ok then check the fuse in the radio module which lives under the plastic floor panel (which you have to remove 3 bolts under the spare wheel cover to release the plastic floor cover) the radio module is the unit with the large black multiplug and a small black antenna cable. There is a fuse in the top of this unit you need to check this one as the amp recieves power through the radio module. The radio module controls all the audio in the car (not the sat nav unit as most people think) all audio no matter from which source is comes from goes through the radio module. If everything is getting power e.g you have DSP on the nav screen and the fuse is ok then you may have a problem with the radio module itself, again with it being in lower area of compartment then it may have suffered from water damage, This is a very common fault with theses vehicles. Let me know what you find.
Matt