Why has the backlight on my display gone dark?

Over the last six months the display on my powerbook has gone dark at various times, but moving the display slightly caused the light in the display to come back on. Now the display is permanently dark. You can see the computer output (desktop, windows) darkly or with a flashlight, but there is no backlight for the display. (A light against the apple on the rear of the display shows through) The computer is working fine. When hooked up to an external display everything is in good order. Is the display backlight broken, or has something in the link between the computer and the display failed? Since the hinge, or something with the hinge, seems to have been the cause of problems during the last 6 months, could it be the culprit? I have been reading about inverter problems or cable problems. Any way to diagnose the actual problem?

As an aside, I just purchased a pram battery and USB board to install since the PRAM battery had failed (date and time were wrong after power loss). I haven't installed it yet. Could the PRAM battery influence the display backlight?