I have had the same problem also since replacing the screen.
I am not certain but i think the problem might be a screen protector on the inside sensor porthole - one which needs to be peeled off before installation. I tried doing this before fitting the new screen but couldn't just peel it off. I ended up sort of scratching it off badly with some bits left behind.
Either way it still didn't work for me but if what people say about screen protectors is anything to go by this could be an issue.