Model: Late 2009 iMac 27" A1312 2309 (Core 2 Duo) Need some help please. I woke up one morning recently to find my iMac was dead to any input. It was working fine the night before, I didn't shut down and just let it go to sleep on it's own. There is zero response when the power button is pressed, no boot chime, no screen response, no fans/hard drives spin… nothing. What I've tried so far: Different power sockets, different power lead Reset SMC Replaced PRAM battery Replaced iMac power supply Removed graphics card There is only one diagnostic led lit on the logic board (labelled LED601) when the iMac is plugged in: There are 4 LEDs in total and it's the led furthest from the board edge that lights up. Strangely the service manual for this model seems to list the LEDS in an opposite order to my board: I assume the LED that is lit up must be LED 1? ( indicating that trickle voltage from the power supply has been detected by the logic board). Does this mean that it's most likely a logic board fail? why would the logic board suddenly fail overnight when iMac was sleeping?