With the camera on, try shining a torch (flashlight) at an angle close to the screen and check if you can see any images at all in the screen.
They will be very faint so trying in a darkened room may help to see them if they're there.
If you can't see any images then there is either a motherboard problem or a screen problem
If you can see images then there is a backlight problem. Either no power to the backlights from the motherboard or a faulty screen.
Looking at an image of the LCD I would guess that the 2 wires shown highlighted would be the backlight power wires.
Check that the flex cable connector ends are clean (gently wipe them with a Q-Tip moistened with Isopropyl Alcohol 99%+) in case there are any greasy residues on them from being handled etc and then carefully reinsert the cable into the connector on the motherboard and check.
(click on image to enlarge)