Default [Q] HD+ screen death

I am (was) running a HD+ with N2A 4.4 . This unit had a damaged digitizer replaced from a parts donor with a broken chassis. Everything was running no problems until a few day ago. I put the nook down before bed and in the morning the display will not work. I get back light, but a blank screen. i tried all the various button pressing combinations to no avail.
I plugged the unit into a PC and can view the nook drive and SD card memory.
I called B&N support and they suggested letting the battery run dead, and then charging it.

After all this I tried to swap out the main board hoping that this was the part that died because I have two of them and all etc.

anyway no luck with the black screen. In the parts of the cracked screen that still work I get full boot on both boards, that leads me to believe that the screen has died, is there any other potential causes or is it just a good old hardware failure?