i put my g5 to sleep before heading off to bed last night. when i awoke this morning, i heard this really loud, fan like noise coming from my g5. it was so loud, i thought it was from outside, like from those construction-type machine. anyways, i couldn't wake the g5 up from sleep. the fans were running super loud. i had to power down by holding the power button down. any ideas as to why this happened?? or what it means? has this ever happened to anyone else?