I've got an iMac, (the swinging arm kind not the newer one). It has been ok since purchased, but recently it has been shutting down by itself. Has anyone else had this problem? I hear it may be a thermal issue, a PRAM issue, an overloaded FIREWIRE bus or USB bus, or the logic board or PSU. Those seem like obvious choices. Im looking for any hard line experiences from anyone out there regarding this. It shuts down at no particular time length or CPU activity. I could be running Photoshop with some heavy task or nothing could be open and it shuts down. Any insight would be appreciated.