The phone does'nt wake up, screen is black

Hi,

I have to repair the phone of my girlfriends dad. It is an iPhone 5

He pinched the phone between the cars door. now the backplate is bent a bit and the screen doesn't fit any more.

He told me that the phone was working a few day's after but now it is completely dead.

So what i tried to do is to change the battery and charge it.

It is now working and i get the information on itunes that the phone is connected.

But it always make the sound like it gets when you plug it to the charger. The sound comes every 30 seconds.

I also tried to change the dock connector, but it is still the same.

I also tried to change the display but it is still a black screen.

Does anyone know what to do?