squares on the screen after battery replacement

Hello everybody.

I recently got an iphone 5s with a broken screen. I ordered a screen online and replaced it. It worked perfectly well except the proximity sensor that was not switching off when calling.

After a quick search online I managed to find the issue and I decided to order a new battery as well as I though mine was not lasting long.

I received the battery yesterday and opened the phone again, I replaced the proximity sensor and changed the battery of the iphone.

When I reassembled the phone and turned it on, I had some squares displaying on the top of the screen.

I though it was because the display connector was not properly connected, so I disconnected it and reconnected it. When I turned the phone on again, the squares are still showing up.

I took a photo of the screen displaying the square, you can see it here http://postimg.org/image/h7kq92sy3/

According to you, what's wrong ? What should I do ?

Thank you so much for helping me