Just like you; replace screen and no back light. So it turns out that the back light fuse is not blown. There's a little piece of black tape that covers the back light sensor underneath the ribbon that is attached to the frame. Put the black tape back just as the original was and the back light will work again.
I found that my lines were coming from the bottom part next to the LCD connector. It's not a connector but it's suppose to sit flat. The gap is what was causing the lines in the screen. I put electrical tape on it to hold it down and I haven't had any more issues. See image!
I tried the hard reset as well as making sure there wasn't any damage or debre on the connector. I've even tried restoring the iPhone and that didn't work. Replacing the logic board is too expensive! I'm at a lost!