no power to ceiling fixture

I think an electrician created a problem when he put in a ceiling fan in the living room. Now a ceiling fixture in the basement has suddenly quit working. There are three black wires connected to the switch. When I touch the leads to the top two wires, I get a light on the tester. not sure if that means anything. I get nothing when I touch the leads to the bars wires at the fixture. There are a couple of white wires that dead end in the switch box. I there anything I can try to restores electricity to the fixture? email is [email protected]