Hi Night Striker,
As long as an external monitor that is connected to either the HDMI or VGA interface works fine, the problem does not seem to be related to the GPU. You already replaced the cable, so the only item that seems to create the issue is the LCD itself. Like Claes pointed out, it is likely that the controller is defective, hopefully the controller on the back of the LCD panel.
Here is what I would do:
1. Checking on the new LCD cable that it is correctly installed.
2. Getting a new LCD screen, for example [http://www.ebay.com/itm/New-15-6-LED-LCD-screen-for-ASUS-N53SV-N56VJ-N56DP-N56VM-N56VZ-DS71-N53JF-N53SM-/400308296983?hash=item5d343bdd17:g:1oMAAOxyaxtTleQ1|here].
Steffen