No airport card installed!

Unfortunately, there are 2 main reasons for this message:

1) The AirPort card has failed and will need to be replaced

2) The AirPort card is not making good electrical contact in the socket where it is installed

In either case, this is a job for a service shop, so you should take it to an Apple Store....if you have one in your area....or contact Apple Support directly for options and instructions.

http://www.apple.com/support/contact/

What did it for me after everything else (SMC, PRAM reset) failed was to reinstall my system using the original disks that came with my computer. Back up your important stuff first, of course.