In this case the logic board needs to be replaced Update: It isnt the video card or display or inverter. The 3rd LED never lit up that means you need a new logic board. But first, i would try pressing the SMU button (Below internal power button) just in case the system just needed a reset. You probably already resolved this issue, but im putting this here for anyone else who comes across this problem.
Answer to: Why is my display not coming on?