Cannot get picture on tv after replacing board with a known good one.

I have a'''Samsung UN55NU6900FXZA that when I turn it on the backlights flicker on and then off, there is also no sound. The on button flashes twice when the blacklight comes on. I replaced the board with a know good one and its the same thing. I removed one ribbon cable and nothing, but when I reattach the cable and remove the other ribbon cable the back lights stay on and the tv has sound but still no picture. Here is a picture of the back of the tv and the board with the offending ribbon cable not plugged in… Anybody got any idea what the problem is?

'''