blue screen of death when engaging reverse - reverse sensors work just screen goes blue (No Camera) screen works fine in forward gears - any ideas?

Blue screen means no input on that connection. Camera failed, camera has no power, camera input on display failed or disconnected, camera harness in boot lid faulty connnection?

blue screen is indicating that the head unit is receiving so that's a good thing. Either your camera went dead or the camera power (most likely) is dead.
Check the fuses I would say.

Also, it would be beneficial to name the model and year of your car.