Wifi
Why is it showing Wifi No hardware installed So suddenly?
MacBook Air 13″, macOS 10.13
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Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode?
Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.
Have you done a PRAM reset, CMD+Option+p+r...
http://support.apple.com/kb/HT1379
In fact, do 3 in a row, takes a bit of time.
Intel-based Macs: Resetting the System Management Controller (SMC)...