my xbox 360 keeps turning itself on whenever it feels like it. i had to unplug the power supply to make it stop. once i get it to stop doing that if i put a game in or something it will do fine for exactly 20 minutes, after 20 minutes it dings four times then the tray opens and sometimes after a minute it will close and other times it wont close. then it does it at random after that. i tried resetting the touch buttons and cleaning them with no luck. help please. if it had to be sent to service about how much is that?