Q: No airport card installed

Delete /Library/Preferences/SystemConfiguration/NetworkInterfaces.plist

Then restart your Mac could solve your problem.

Open Treminal.app, then type

"/usr/sbin/networksetup -detectnewhardware"

Which means to detect all hardwares related with networks, both wired and wireless.

"Treminal" was a typo above.

Open Macintosh HD > Applications > Utilities > Terminal

Careful though, with Terminal. You need to know exactly what you are doing before doing anything.

Sorry for the typo...

For more detail, read here.