Also it is not directly related to anything you did. When you have such bad apple it happens sooner or later when you reboot the device. How long are you using your device? Most often it happens in first days of usage (perhaps depending on how often you reboot).

BTW igor, can you say if it is caused by bad display or by something else that 'fries' the display? i.e. does new display without this (latent) fault fix the issue completely or can this n770 kill another display with higher probability because the problem is in the board or something.