My iphone 4 screen cracked.i had it fixed.everything works but the Wi-Fi?

I go to set up the Wi-Fi but it doesn't recognize anything.

Most likely broke the Wi-Fi antenna when the screen cracked or when it was fixed. I'd send it back to the repair shop.

The Wi-Fi not working is one of two things. If the Wi-Fi is grayed out in the setting menu on the phone there's no fixing it. If is is just not picking up the signal like you said. Who ever fixed your phone is a scam and don't know what they are doing. They didn't connect your Wi-Fi antenna.

Also I've repaired hundreds of cracked screens and never NEVER have I had a screen crack so bad to break the Wi-Fi antenna. I've even had a phone come in after being run over by a USMC HUMVEE