The same thing happened not too long ago. I installed four recessed lights and a switch. When I tried to get them to light up, they just wouldn't. I have verified with an electrical tester that there is electricity in the hot wire at all four fixtures and that the switch is wired correctly. My first thought is that polarity was reversed, but that's not the case. The recessed lights (same model) attached to the other 2 switches in the same box are working just fine. I got annoyed and just went to buy new LED flood lights.