iPhone 6 wont turn on after battery replacement?

My iphone 6 would die quickly after a full charge. I decided to replace the battery myself, so went ahead and bought a replacement battery through ifixit. I followed the instructions on the webpage. It turned on but I turned it off to double check everything is ok now it doesnt want to turn back on. I cant use the old battery because it was dead. Sceen doesnt do anything. This isnt the first time i open an iphone so i know to be extremely careful when opening it. I also changed a battery of another iphone after this one and works perfectly!