- did you get your screen from China? Its the digitizer. Appears to be "side lit" not "back lit" if you order another screen (usually happens with the color screens.
- I use replacements from sunsky-online.com I have never had an issue and they are $30. Heck if they dont work you could buy 4 screens for ifixit price
- The ribbon cable may have been compromised on the digitizer. I had the same issue and replaced the screen with a different on and worked meaning the problem lies with the digitizer or front display assembly