problems with g5 powermac 2.0 dual

hey guys!

i've been having some problems with my dual 2.0 ghz g5. sometimes the machine wakes up from sleep by itself and it doesn't know how to go back to sleep afterwards. my buddy was sleeping over the other night and he woke up in the middle of the night. he was using the other computer when all of a sudden, my g5 turned on by itself (he got freaked out by that). any ideas what might cause that?

this morning, when i woke up, i heard a really loud sound. my g5 woke up in the middle of the night by itself again and this time, it sounded like the fans were all on at full. it was very very loud. i tried to shut it down but the computer didn't respond, so i had to manually hold the power button to turn it off. i think i've had this hapen once before too... any ideas what might be going on here? thanks guys!