[TimW]

I'm concurring with Dr. Crib, it sounds like a broken screen. It doesn't have to be a blow or a crash to cause the thin glass substrates to crack. Enough pressure on the screen will do it. Twisting will do it. Oddly enough, you can do fatal damage to a screen and the frozen image doesn't emerge immediately. I had a K3 that I dropped a few years ago and the frozen image didn't show until several days later. Imperceptible damage to glass tends to travel. I'd love to tell you that Kindles are different...they aren't. They use the same eink screens as Kobo. Unless the eink screen is one of the new bendy types (very expensive), they're very prone to breakage.