I have a nexus 7 I also have a hipstream eclipse rotating case for it that has magnets on it. we inadvertently put it on so that it closed from the right and folded under with the magnets on the left. this caused it to quite often shut down we turned the cover around so that it covered from the left like a book. the magnets when it is closed not only held the cover in place but also when you close it, put it in sleep mode, which it is supposed to do. if the magnets are on the left side it will shut it down, which it is apparently supposed to do or just does. so if you are having black screen problems check to see if you have magnets, and ensure they are positioned on the right side when it is closed.