digitizer not lighting up /not dipalying /stay dark.

i already order 02 digitizer and screen to replaced my old one(broken one ) . but on both occasion after replacement when i turned on my phone the screen stay black ,not light coming on the screen nor display. but when when i put the old one back on ,the light come on and it displays at least but can used it because digitizer is bad obviously.

is there a step that i am missing? is it some kind of reset that need to be perform ?

please i need your help can afford a phone right now.