If the computer's booted, and you're getting a functional desktop on the external display, then the problem is related to the standard display. I would recheck the display cable connection (and the cable routing) at the logic board. It's a tight fit and a short cable, and there's really only one right way to fit it through the hinge.
You may have to replace the display cable, which is a fairly ugly job. As an experiment, try launching Photo Booth and see if the camera mounted at the top of the display still works. The cable assembly that carries the camera signal is joined with the display cable, so damage to one may appear in the other.
The Airport/WiFi and Bluetooth antenna cables also go through the hinge; do those functions work correctly? Hinges do tend to loosen up through repeated use, and that increases the risk of cable damage. It might be worth checking the left and right hinges, while you're at it.