Why won't my kindle fire hdx 8.9 turn on?

I was using the tablet, then suddenly, the screen went black. the backlight remained on for about 7 seconds, then it turned off too. this happened several times. if I didn’t touch it while the backlight was still on, it was fine. I would just repower it once the backlight turned off, and it would come right back on, but when I tried to reboot it while the backlight was still on, it wouldn’t reboot. that backlight was the last sign of life the tablet showed, because, after that, nothing I tried would get it to turn back on. I left it on the charger overnight, I tried holding the power button for 20 seconds, then tapping the power button, I even took it apart and unplugged the battery to get it to reset, then plugging it back in after a time, but nothing works. if anyone has had the same problem and has resolved it, I’d love to hear what you did to get it up and running again! thanks.