Maintenance of iPhone 4 - Assembling it back

Hello all,

Long story resumed: I've got an iPhone 4 that, at least in the beginning, seemed a steal.

The device suffered from a serious fall (2 stores tall is what I have heard). My manager told me if I could recover the stuff inside of it, I could keep it since he already had bought another one for herself. Job done, she got her pics and I got myself an iPhone 4. Of course it was in shambles, so I got a new screen (the old one even got the flat cable ruptured) with the necessary tools to try and assemble it back.

I assembled everything as per instructions of iFixit and the iPhone still won't show any image. The display has been verified and tested by my supplier, so it's obvious the problem is on the device.

Sure, not everything is flowers, there are a few missing components which are coming later on (vibrator being one of these and the Speaker Enclosure other). Also, I'm missing a few screws. Still, the device IS booting up. I even got it listed under iTunes.

And so, my question is: could there be anything else making it not show any video on the display? Do I have to assembly it completely in order to provide some kind of "contact area" the display requires to start its magic?