Replaced display and lcd, but still doesn't function

Hi, My dad dropped his s4 while riding his motorcycle. The screen was completely smashed. I took it apart, and repaired the display and lcd. Prior to removing the motherboard, I tested the replacement screen and it worked with out problem. I carefully disconnected all parts from the old one, and put it on the new display assembly. It was tedious, but I did it! Yay! However, after all connected, battery in, and turned on, all I get is sound, and the blue indicater light. No other power on the display screen. The indicater light goes from blue to green, then nothing. I took it all apart amd started over three times. I even bought another display and the same exact thing. What in the world is wrong with it? A cable? Some plug that isnt installed correctly? Please help!

Thank you!