works for a while then cuts all power to the the cpu,
i'm having the same problem with 2008 / 3.1
works for a while then cuts all power to the the cpu, light stays on at the front and the graphics can fan goes into overdrive, but there seems to be no power to the main body , also noticed that the psu fan stops working. i have run apple hardware test and it all seems ok . sometimes it stays booted for hours other times it just cuts out at the end of a reboot. I have noticed that I can force it to happen by using lightroom or other Raw editing software , but it can just as easily happen when i'm browsing the internet.
I was thinking it might be the PSU but this seems to be the only thread i can find about Mac PSU problems. mouse scrolling activity does seem to trigger it more often then not.