iPhone 6 plus not working after screen replacement

Hi

I tried to repair my iphone 6 plus rear camera, however I did this whilst the battery was connected. I disconnected the screen to get better access to the camera, I then reconnected the camera and the display was working perfectly fine, however there was white lines on the screen, I have seen forums where if this is the case you need to disconnect the screen then reconnect it. I did this but then the screen lit up but was completely black.

I then disconnected it and connected it again but this time the screen did not fire up at all. I am currently getting no response from my phone and even when I connect it to laptop nothing shows on iTunes either. Please could you tell me what can be wrong with it and how to fix this too ?