New Screen not working

I recently bought an iphone 6 plus from ebay with a smashed screen with the hope to replace the screen and use it. The smashed screen works, except from the touch doesnt, so I can see that the phone powers on as usual, battery holds charge etc. When I first replaced the screen, I got no reponse from the device, I thought I had damged something, but when replacing the original screen, it still powered on. I tried again, but still no luck, so I returned that screen assumong it was faulty, I then ordered another replacement screen, with the same problem. Am I just really unlucky and have had two dodgy screens or could there be some damage to a connnector I am missing? I dont think however this could be damage to a connector or otherwise I wouldnt get anything on the broken screen. Please help! Many thanks