Why will my Nook HD display nothing but a black or blank

My Nook HD suddenly went "black" after I put into sleep mode. The screen will still turn on, the backlight is displayed, but nothing more than that; a black screen. I've tried hard resetting and holding the buttons for 20 secs method multiple times, still nothing. At one point it entered "explore by touch" mode (distinguishable by the audio messages it was playing) so the touch screen is still responsive. I did nothing with the software of the device, it was running whatever the latest software B&N put out for it was.