I had the same problem with my son's device. I found there is a setting that requires the power button to be pressed twice and held for 2 seconds. I didn't change the setting to that. It came that way. You can change it under settings. Anyway, try pressing the power button twice and on the second press hold for 2 seconds. It took me 3 tries to do it just right, but it finally worked and I immediately went into settings and changed it. Good luck.