Help - Radio completely dead after installing Phatbox

I plugged in a Phatbox yesterday in my wifes A3 (2000) and it worked fine. Took the cartridge in and loaded up with toones and plugged it back in today, but the system is completely dead, no phatbox, no radio no nothing! I even plugged in the CD changer again but no life in that either.

I plugged in VAGCOM but that couldn't even connect to the controller, so I guess there is no power. Checked the fuse and that seems fine though. Any ideas what it could be or where to look next??

The only other thing I did was remove a sidelight bulb, but surely that would have no effect?

bought the removal tools today to check the HU fuse, and yes it had blown. Well done Andy! Borrowed the fuse out of my HU and plugged it in only to see it glow a nice orange for a moment - so now neither of us have toones!

I'm hoping it's just a wire come loose in the boot connector as I had to struggle with it to plug it in due to having no slack, otherwise I may have a problem with the Phatbox. Will buy some fuses tomorrow and investigate further.