Peggy, a new video cable will not "fix both screens are now black" the video cable is only for the internal LCD and do not connect with an external monitor. It does sound like you are having issues with the GPU circuitry, your computer does not have a separate video card. Your video card is integrated onto the logic board. So in that case you would have to replace the mother board. Since you took it apart, I would definitely go back and examine every connector and double check your work.