Hello J.P.S
Thank you for your reply, The demo kindle has the settings option greyed out so I cannot get the serial number, (short of connecting a serial connection to the mobo and reading it off during the boot).
Of course if the demo kindle can be un"demo'ed" that will also do as a fix

The two screens look identical, and connect the same to the mobos.
I assumed it would be a simple swop job as I have swopped screens on my sons keyboard kindle and his kindle 4 in the past with no problems, its just my luck that my paperwhite is not playing ball!
My worst fear is that amazon have serial numbered the screens and locked the screen and mobo together in the software.