I know this post it old, but just to help anybody that has similiar issues. More often than not, the problem is the dc-in board not the logic board( alot cheaper to replace than a logic board). How you can tell is if some of the usb ports dont work( use a laser mouse so you can see the bottom of the mouse light up so you knows its working, or if it doesnt light up you know its not working) and if it boots fine to an external monitor.