Same here, happened overnight the day I updated OS software. Turned off then next day turned on. Found this question often enough in forums but no solutions. Have tried resetting, Diagnostics, Assist Me, deleting network, adding back in, deleting location, adding location, permission repairs, borrowing disc from my iMac and MM to repair, tried to reinstall OS with remote drive but it fails to get on with AirPort and I don't have ethernet. It can find and connect to both MM and iMac but cannot get on my network. Tried resetting Verizon FiOS router. Tired all just posted more than twice, some mor than 10 times. Tried over 3 days. All other devices and computers (11 total) can get on. MBA just times out and shows greyed out wireless signal icon with exclamation point.
Once, it even froze up and refused to accept any keystrokes when entering network name and password. Another time it started spinning and displayed message that it was searching for a bluetooth keyboard and mouse (??MBA doesn't have that as it is integrated!).
I am ready to trash it after 3 years and go back to PC notebook. Really frustrated with Macs and Apple philosphy right now.