Hi, i changed do another ribbon with the same wiring as you, but now, when i connect it, and powered the LCP17, the led on the LCPxpresso flash one time, and nothing more, maybe my ribbon is bad, but after verifying the shcematic, my first ribbon was good. so it's not a ribon problem.
i mesured the pin with my multimeter :
On the LCP17 :
Gnd - Pin 15 = 5V
Gnd - Pin 16 = 0V
On the screen :
Gnd - pin 15 = 4.79V
Gnd - Pin 16 = 0.11V
But i don't have any backlight !!
So i claim the problem is something like MaG2k said, it's a brigde or not ? but which one, i don't want to burn my screens, but bridging something wrong.