If it is similar to the j3, the screen is above two sensors that look like small circuit boards. I replaced a screen a while back, and ran into the same issue. I took the screen back off and re installed it. I made sure to line the groves on the bottom of the screen with the small touch sensors. It fixed the problem for me. When installing a screen you should always test it first. You can plug the screen in, turn the phone on, and dial *#0*# this will bring up several test options. The touch test will allow you to test the digitiser, and the subject test will let you test all the buttons including the back and apps button