Check in your System Profiler/Network tab, and click on Airport Card. If it says something like 'no information found', then your Airport card in your Mac has died and should be replaced.
If you know how to get at your Airport card, you could try reseating it.
If you think the System Profiler is lying to you, then reset the PRAM (reboot while holding Option-Command-P and R). You will hear the startup chime. Continue to hold those same 4 keys until you hear the chime 2 more times. Check the System Profiler again. If no difference, then it's possible that the OS X install missed picking it up during the install. Do an erase and install (you just did this, but could be a faulty install). Watch for any errors during the install. If that is no help, get your Airport card replaced.
Serendipity is a lucky guess !