Screen / buttons / DVD unit / USB sockets no power

Ok so I’ve got a problem with our 2012 evoque in that the touchscreen is not working. Not been on here in ages since I gave my wife the evoque when I got a Jaguar F-Type.
The screen won’t light up at all, no lights on the screen buttons (but the LED for the parking sensors does work). It was sort of working / sort of failing for a day or so but then packed in completely.
There’s a cd in the DVD / Navigation unit which won’t eject.
No screen power and no sound.
Parking sensors and rear camera don’t work.
USB sockets don’t work either.
Heaters and controls still work fine.
I’ve tried a few things- all the fuses in the rear fuse box are OK, as are all the ones in the glovebox and all the ones in the engine bay.
I stripped out the DVD / NAV unit (behind centre console) and it looks like it’s still getting power and have stripped out the screen itself which also seems to be getting power but not turning on.
I then tried replacing the DVD / NAV unit with another one from eBay and no change. Same with replacing the screen with an identical one- no change.
I’m a bit lost regarding why this is happening. The vehicle is long past warranty so I’m keen to see if I can sort this out myself. I’m thinking that next step is plugging in a diagnostic kit and seeing is there are any major errors coming up.
Thanks for any advice anyone can give me!