HTC ONE M7 BLACK SCREEN help please

[JBMF90]

Hi guys, I've recently bought a working htc one phone but it needed a new front replacement. I bought a new front replacement and I swapped all the components from the old front to the new. I go to turn the phone on and all I am getting is the flashing back and home buttons at the bottom of the phone, it vibrates, but other than this i can't seem to get the screen to light up or even work at that! I've tried holding the power and volume down buttons and tried a bright led light over the proximity sensor but still no luck so before I give up all hope with the phone could someone please help me try to resolve this problem? many thanks.