So I have searched for an answer to the iMac self shutdown and all the threads I have seen have given no answers. My early 2009 24" imac started shutting off on it's own a few months ago and it progressively got worse until now I will not last more than 5 mins. I replaced the power supply which did nothing. I replaced the logic board which did nothing. I replaced the hard drive which did nothing. So now I am at a loss. If it isn't one of those 3 then it must be something small and stupid but I can't figure it out and the 'genius bar' is no help either. Obviously no warranty but I am not afraid to fix it myself if I just knew what to fix. Any help would be appreciated.