My iPad air 2 refuses to fully boot after screen replacement why?

my iPad air 2 is not booting fully, it only shows the apple logo and go off.

this happened after i replaced a new screen, But the old broken screen steadies when power on though i cant see whats on the screen because its broken.

i have tried...

1. new battery

2. another screen

3. i have held down the power button and the home button at the same time many times as i can count

but yet no good result please what do you suggest i should do again?