David, my Zenpad S 8 showed weird rainbow colors & was unresponsive to touch before it went black. Upon rebooting, like you said, I could tell (especially in a darker room) via the backlight that it was on, and using the volume keys the speakers responded also indicating it was on. I will need to contact Asus & send them a video of what's happening, but for now I have discovered a temporary solution. Believe it or not, giving a hard rap with a knuckle or two in the center of the back of the tablet springs the display back to life. I'm guessing something must be connected poorly in the inside. Give it a try.