I replaced my phone battery, but now the screen is unresponsive. Help!

Check all the ribbon cables and ensure none of them are ripped or damaged, they’re very fragile. Then check all the connectors themselves for any bending or damage. When you connect the screen connectors, be sure to press in first on one side, then the other. Don’t press in the middle or they can bend. They should click in on both sides.

Then restart your phone, try a hard reset by holding the Power and Home buttons simultaneously for 15 seconds or so, that can occasionally clear up issues.

Unfortunately if none of that works, you might’ve really screwed up the screen somehow, the only fix is probably going to be a replacement.