Will not charge! Stuck on low battery icon.

Bare with me, this is for a friend and hes kinda !#^&@@, so someone please HELP!

Okay, so... I done a repair for a pal. It consisted of a charge port replacement because his phone wouldn't charge properly. (he had to mess around with the cable alot to make it charge).

I tried all the obvious things first like removing any debris from the port all that stuff. No results... So I thought f*** it and just replaced the whole charge port unit itself. I then plugged in the charger to test it and it worked absolutely fine, I plugged/unplugged it a few times just to see that its definitely going to work still, and it did.

Next I unplugged the charger and screwed the metal plate down on the lcd/digitizer/camera cables, (while it was still turned on, I probably should have turned it off first), Before I closed the screen down I pressed the power button to see if the phone was ok, The display and everything was fine.

BUT THEN... As soon as I closed the screen shut and screwed the two bottom screws in, the phone went completely DEAD!

So I opened up the phone again, disconnected the battery connector, reconnected it and then pressed the power button again.

It came back on! Great!

So again I put the screen down, screwed the bottom screws in and it worked beautifully.

I gave the phone back and then drove home. 5 minutes after I left I received a text saying the phone has died again, so he plugged it on charge for half an hour but only the low battery icon would come on.

So today I went back round his house, opened up the phone again once more disconnected the battery connector once again and connected it again and tried the power.

The phone kept doing the same thing over again, it came up with the low battery icon wit the picture of the charger. So I plugged in the charger and its still stuck on the low battery icon. IT WILL NOT COME BACK ON!

Now a few things to consider that will narrow out the possible problems.

- First of all, there is NO lint or damage or anything inside the charge port, this was a brand new charge port that I installed myself, 100% no damage at all. So its nothing to do with the charge port.

- Hard resetting is totally out of the question. I have plugged it into itunes, tried holding down the power button and home button to bring the itunes icon up about a thousand times but it will not bring up the itunes icon what so ever.

- I have checked the contacts of the home button, they look fine - no damage, so thats not the reason why the hard reset option wont work

- itunes DOES NOT recognize the iphone when I plug it in no matter what you press, nothing comes up, I hear no sound when I plug it into the computer, itunes just simply isn't communicating with the device.

- I have also tried connected to itunes on two different compiters so Its nothing to do with itunes either. (Both were up to date)

- I have also tried sticking down a little bit of tape over the battery connector to eliminate any possible grounding issues that could be short circuiting the phone and shutting it down, its NOT THAT either.

So what on earth is causing this problem???

One thing I haven't tried however is replacing the battery...