I'm having the same problem. Replaced the charging port but it still won't boot past the white ZTE "powered by Android" screen, then shuts off. Holding the power button just returns it back to the white ZTE screen.
it turns out that there are 2 magnets that must be swapped from the old digi to the new one. I assume they work with magnetic screen covers (when you cover the screen it shuts off). Anyway, I took the old magnets off (a step i missed in the guide) and put them on the new digi and it works perfectly. Mission accomplished.