What could be wrong with the iPhone?

So I took the iPhone with someone (an establishment in a mall) to get it fixed because the screen was broken. I picked it up and the guy said everything was fine and nothing was wrong. Obviously I believed him. So I went on my way and when I arrived home, I tried connecting it to my Wi-Fi and to my neighbors Wi-Fi and nothing! It wouldn't even find my house Wi-Fi. I went real close to my DSL and that's when it found the Wi-Fi. What could be wrong? What did the guy who fix the screen, mess up?

I'm considering taking it tomorrow first thing in the morning!

He doesn't know how to do his job properly

Well if he did mess the Wi-Fi up, the thing that would've been disturbed is your Wi-Fi antenna. That's not really something you can fix at home, so yes take it back if the problem keeps persisting.

It's possible that your antenna got damaged or disconnected when the person replaced the screen on your iPhone. IPhones have an antenna that is located on or near the screen.