Well you tried everthing I've seen or could think of... though leaving it on till the battery runs out would be a curious test? If it will even do so.
Edit: You didn't state how long you tried charging it for. If it drained all the way it can take a good amount of time and WILL get stuck at only the backlight just like you have.. The charging symbol shows up later and will finally boot at around 15%'
HTC sensation 4G | Revelation ROM (Calls don't go to missed upon answering thank you very much.)
Nook HD+ 32 | Emmc cm10.2 ROM, Ubuntu touch 14.04 (Rock solid - up time 120 hours? Check!) (MBG4GA, 0x000015)
Replaced by above: Nook HD+ 16 | (Testing finished - random reboot results: defective tablet) (MAG2GA, 0x000015)