iPhone 4 wont turn on even after new battery?

I bought a broken iPhone 4 it had a cracked screen and wouldn't turn on unless plugged in. On further inspection I also found that wifi doesn't work as it says n/a in the about section of the phone. I replaced the screen no problem and inserted 2 different new batteries only to find that a new battery doesn't work. So it won't turn on unless plugged in and wifi doesn't work. The phone appears to have no water damage as far as I could tell. I haven't come across a problem like this yet, any tips or solutions?