I've had this happen to me twice but i have been known to leave my console running over night and it not to happen. I know there is a setting on the machine somewhere that lets you specify auto-shutdown but i doubt it's anything to do with that. Could be faulty tech...it is Micrsoft after all and i'm 7 machines down and counting...could be an issue with the pad although i don't think holding the xbox button for hours is supposed to have any effect. All i suggest is carrying on regardless and bear in mind you might lose your place if you have to go out and plan accordingly.
