John bought an iMac in 2011 and lately it's starting to flicker, with half of the screen darker. He called Apple and they suggested clearing the PRAM. Leo says that's one of the magical 'voodoo' techniques in case something got corrupted like a driver or something. Then they had him do a factory reset. But it still is happening. John also heard that the video card may be going out. But more likely, Leo says that the backlit LED screen simply stopped working, and that can happen over time with an LCD. One way to test if it's the video card is to connect an external monitor to it. If it works, then he'll know that the video card is fine and the backlight is out. Is it worth repairing? It comes down to how much it costs to replace and often times it's not.