Why won't my phone turn on?

the lego connector inside teh phone where the battery sits is delicate, I would reopen the device take out the battery connector check of any dust or (happened to me before with my iPad repair) the replacement battery may have a clear protective film over he battery connector to protect it dueing shipping. if all looks ok, clean the connectors (compressed air will do) and ensure teht the battery is clipped in correctly, if not then it may be a duffed battery, if you still have it, put in the old one and check again, if it boots then send the dud back, if not then you may have dammaged the battery connector during the repair.