Original post by: remacberlin ,
These machines have diagnostic LEDs on the logic board. You'll have to take off the front glass (suction cups required) and front bezel. They are located on the right hand side underneath the screen, you may have to move some cables aside to spot them. The first one should light up when the computer is connected to a power source. the second one should light up when you press the power button Number three and four are video related and show you if the graphic chip is initialized and wether there is connection to the display.