I reassembly the phone: nothing work!

Hi all guys,

First of all sorry for my bad English!

My girlfriend has an iPhone 5C with just an old battery that must be replaced and the glass of the screen that is a little bit over its original position. Yes Man, it's easy ;-)

So I have bought a new battery and the 3M stick for the screen.

1) I opened the phone and disconnected the screen (flat cable of sensors​, LCD, touch)

2) I replaced the battery with a new one

3) I disassembly the glass of the screen with hot air and repaired it.

4) reassembly all the phone

Now begin the best

5) at the beginning the phone start ok with the white Apple and it shows the pin dialog over the home. All ok.

6) when i try to enter the pin i find out that the touch screen doesn't work. LCD and all the other things are ok. Battery is charging ok.

7) I disassembly the phone and to power off it i have unplugged the flat cable of the battery. So i have re-plug the connectors of the screen.

8) power up the phone but LCD doesn't work. Just the back light..

9) so another time disassembly and reassembly the phone, sure that the problem was related to flat cable

10) i have restart it but the phone is off. Can't do anything. Now even the back light doesn't start.

I've try for 5 hours to find a solution.. But not. I don't know what to do and I'm desperated.

Just the last thing: one of the time that i tried to power up the phone the LCD showed the white Apple while the screen was open. Moving the screen (i think the flat connectors) the Apple disappear a little untill it turn to black screen.

Where is the mistake?

How can i fix it?

Thank you very much