Not working phone after drop

Hi.

I just bought a cheap broken Iphone 6 from someone i know. She dropped the phone, and the screen was cracked and the phone was "dead".

They had tried everything they say, connected it on a computer to get pictures backuped.

First thing i did when i bought it was to test another broken screen, the phone booted up normally, and everything seemed to work fine. (a very good deal for me)

But when I connect the home button flex on logic board everything goes red. And if i turn the device off and connect the flex, it wont turn on.

I also found at that the old cracked screen works well if the home button flex is disconnected from the logic board.

EDIT:

No physical damage to the ribbon cables on the home button flexes whatsoever.