I agree that you will need to replace the logic board but understand that the cinema displays logic board will after a time require more power to enable it to switch on. This is not a problem in the newer displays as you are able to plug the kettle lead straight into the back of the display. The older cinema displays eventually degrade and although it will still work you will need to provide extra power. (EG: 19" display will work initially with a 65w charger but once it starts to degrade it will require a 150w charger just to get it to switch on) As yet i have no definitive answer to this problem which is why i have ended up on this page. I work for a mac resale outlet and in the 4 years i have been at this company i have serviced hundreds of these displays and they all end up with the same problem in the end.