Chosen Solution
late 2012 Imac 27” screen black. after 1min 20sec. i get a grey column in the center with 2 blue vertical line in a center of the screen. is this a faulty Graphic card or screen damage?
To figure this out you’ll need to connect an external monitor to see if the image looks OK on it. I’m suspecting you have a bad display, but your symptoms also could be a bad logic board.
