Try this if your Apple Airport is off and you can’t turn it back on.

1. Connect to network via Ethernet.
2. Go to Network in System Preferences.
3. Select AirPort and under the gear dropdown choose Make Service Inactive.
4. Hit the plus and add a new AirPort service (Airport 2 or whatever).
5. In the Advanced tab add the name of the wireless network you wish to join.
6. Hit Apply.
7. After a few moments, the new service found my network. I deleted the “original” Airport service and renamed the new one to Airport.

If this works great!