No display, no back light

Hello Ifixit community

I have a problem with my macbook pro a1398

i had a broken display so I ordered a replacement. After I replaced it the bottom 1/3 started flickering after 3 hours after the replacement and the then it stopped like this

then i disconnected the new one and placed the old one, which displayed the old problem

after i disconnected it and attached the new one nothing was displaying, not even back light or image was showing when i put a flashlight close to the screen. So I attached the laptop to a tv via HDMI and everything was working.

So whats the problem now?