the same thing happened to me.
it is usually from an alarm clock that is set.
so, go into your clock and check if you have any alarm clocks set, and if you do, delete them.
also, there is some weird error where a "hidden" alarm clock is set, and this could automatically turn on your 770. to fix this, just go into your clock, and set an alarm clock for any random time, then delete that alarm clock. this should fix it.
it worked for me on my n800...