I have had my iMac since 2005. Almost to the day of the three year apple care expiring I can no longer get my computer to turn on. It was a progressive problem that would result in some success in getting the computer on, until it would no longer come on at all. I could hear a flicking sound in the back and a pulsing noise when trying to push the rear start up button. Is this the logic board or maybe something else? Any help would be appreciated. I want to see what anyone has to say first before I take it to the apple store. Thanks again.