imac problems

[TheFuzz]

at work we use a 17" imac g5, 1.8ghz(build 7w98) that's hooked up to all of our decks for capturing video and film transfers. we also use it to convert .mov's to .flv's, so sometimes we'll leave it running overnight. it's been great until the past two weeks or so where every morning when i get here it's asleep and the fans are running full speed. i can hear them before i reach the room. it won't wake up; i have to force power it down. now, during the day it's begun doing it. is this a common problem for these machines? is there an update that fixes it? it's running 10.3.9. we also have a 20" core duo that's running fine, the only problems have come from the g5.