ha, mine did the same thing, it just started randomly, but would consistantly do it everytime i used it. finally it stopped booting up at all. i sent it in because i bought applecare for it. they told me it needed a logic board replacement, but, they told me it had <em>liquid damage</em> whatever the hell that is. i never spilled anything on it ever, but still, they found some corrosion inside when they opened it up.
i ripped it apart when i got it back home, and i found nothing wrong inside, and i even got it to boot up a couple of times, but mostly, no dice. dead computer.
it looks like i'm just out the 1600 dollars i paid for it too. oh well, my next computer will still be a mac.