SD Card issue?
It looks like it was maybe an issue with the SD card? I plugged the sd card into a Windows 10 computer and had issues reading it. I'm using a micro SD card with an adapter, I unplugged and re-plugged the micro SD from the adapter a few times and it then came up on my laptop.
I re-installed the card in the radio and it booted, YAY!
Then found a firmware update on the Spektrum RC site and installed it following the instructions, after what appeared to be a successful flash, it's still booting up and seems to work fine.