My iPhone 6 now not working at all following replacment screen

Hi, can anyone help please? My son smashed his iphone 6. It wasnt under warranty anymore so I decided to try and fix it myself.

Im generally pretty good with mending gadgets and have had a little experience. Anyway, I purchased one of the replacement LCD's which come complete with the camera and earpiece.

I followed the instructions to the letter. I knew the battery had been dead for a while. My son had told me he hadnt been able to charge it. I fixed the screen and when I plugged it into my pc - it was recognised by itunes but it came up with the error 4005?

Now, alas it is not being recognised at all. No power, nothing. Dead as the proverbial doornail.

I have triple checked the connections and as far as I can see they seem pretty clean, straight and theres no damage.

HELP!

Thank you ;-)