I'm frequently getting the problem that: Many times the screen goes grey and a message box appears telling me that I have to restart. Often this is preceded by the fans gradually increasing in speed until they are runing at maximum speed. BUT the fans behaving that way is NOT due to overheating. I have to use the restart button to make the Mac restart. I have used reset button to reset the motherboard but that did not cure the problem. Anyone have any ideas about how to cure this problem? I'm running 10.4.9. The mac is a dual 1.8 (June 2004). 1.5GB RAM, two SATA internal HDs (Maxtor), two external firewire HDs (Seagate). All the HDs are less than a year old.