Chosen Solution
Sometimes after a couple of hours, more often than not, the iMacs screen start to flicker briefly and then the computer shuts down. It tries to reboot and then shuts down again but sometimes it just stay dead. I have to pull the plug from the socket and reconnect it again to get it to boot. I monitor the temperatures and the only hot part was the power-part and I use smcFanControl to increase the speed of the fans. Then I can use the computer longer before it happens, and it happens less often. It is not a recent activity, but I want to try to fix it if its possible.
This could be several things but lets start with the power supply. To the right of the RAM slots are LED diagnostic lights. You’ll need to remove the frame to get to them. They may have a piece of black electrical tape covering them. They should all be on before it shuts down on you. A restart at this point will help identify what’s failing. Let us know what the lights show. Here’s the breakdown on the LEDs: LED #1 + LED #2 + LED #3 + LED #4 = Power available, system is powered on, video card found, and internal LCD found.
