newbie with MMi problem

[beanmasteruk]

Hi all, looking for some pointers on my 2011 A4 TDi Tecnik. Just bought it and the radio/MMi doesn't work. Powers up for around 10 seconds then dies. No red lights on the buttons either. Checked fuses in both dash side panels and all ok, but found a 30amp fuse in the boot thats blown, F51 i think it is. No handbook with the car so Googled that! Soon as I put a new fuse in that blows too. What can ~I check next to find out why it blows?