Replacement screens don't work (2), original still does

I replaced the broken screen on my girlfriend's iPhone 4s. To my surprise, it wouldn't display anything afterward (first time that's ever happened to me). I pluggged the original screen back in and it still worked. So I fired off a nasty email to the guy I got the screen from and went to a local shop to buy another one. The girl brought out a tester and showed me that the new screen was a good one. However, when I put in this new one, it doesn't work either. It appears I need to eat some crow eith the original guy.

Here's where it gets weird... I read all of the posts about this problem and everyone says to hard reset the phone. That didn't work. Then I tried another solution from a post... I started the phone on the old screen, then switched to the new screen with the phone still powered on. The phone worked. I reset the phone and it quit working. I did this a couple of times with both screens and got the same result.

Is there an issue with some iPhones and replacement screens? Does anybody have an answer?