Well my thoughts that it was inside the screen itself was because he said he can get the screen to flicker by pushing on the lid. If the loose connection was in the body of the laptop that would not have any effect.
Not the lid itself the "lid button" (sorry don't know the technical term) in the corner.The one that tells the system when the lids down for power/action preferences.If i press it in the screen flickers for or a split second on release or in other words when it thinks i just raise up the lid.
I followed you on that part, but still agree with Starfalcon that the screen connector is a good place to start -- albeit start with the one in the base. Sometimes a plug that is coming loose, but is still making a partial (resistive) connection, can exhibit odd behaviors of this sort. Adding to what I said earlier, I'm playing with a balky Toshiba this week and the screen connector is actually under the keyboard. Same disassembly process described above, but then once the bezel comes up, a couple more screws are exposed and the keyboard tray is released. Just got to be careful with it because it usually has a ribbon cable going back to a compression connector.
Since it works fine with an external monitor, might also tinker with the docking and power management settings -- maybe the unit thinks it's docked or otherwise being instructed to kill the display, when it's not.