Steve OE55YHY

HI All, I've just bought an a6 Avant C6 3.0 TDI Quattro. It's a very quiet drive due to lack of music or radio or anything else for that matter.. If I push the screen button to the side of the MMI Screen it comes up with the Audi logo and the center console illuminates for about 30s then goes out. If i randomly jab at the buttons it some times powers up the screen and console, but then goes out again. The CD changer in the glove box has power and makes noises like you would expect. The NAV unit in the boot has power, it ejects and accepts the disc. Previous owner says he changed the PCB in the center console, but not sure what results he had previously. Any pointers greatly received.....