How to Fix Nvidia Shield TV Pro (2017 model) that won't boot past Android Screen
1. Ensure Shield is Plugged into TV with HDMI
2. Plug a micro USB cable into a running PC/Laptop
3. Plug power cord into Nvidia Shield
4. As soon as the Shield lights up with the green lights press and hold the Shield's power button (bottom right corner - it doesn't really look like a button) for approx 7 seconds, at which point you should see the TV screen change to an options menu
5. Tap the Shield's power button repeatedly to get to the bottom option "Factory Data Reset"
6. Long press on "Factory Data Reset "
7. Long press to confirm
8. Factory Data Reset will begin. It could take a couple of hours - go outside or something and check back later!
Before doing this you could attempt to force it to Factory Reset using the Controller. In my case my Nvidia Controller was not connecting to the Shield.