I too suffered the very frustrating “Wifi- No Hardware Installed” for the past month after upgrading to Lion (mid 2009 MBP running 10.7.2). I finally resigned myself to replacing the wifi card. Prior to ordering a new card, I took a last stab. Lo and behold, it has consistently worked for three days now.
Here’s what I tried that didn’t work
Ran Hardware Test (everything checked as okay), reinstalled Lion, Reset PRAM and SMC, deleted wireless locations, reset routers and tried 5 different locations and routers, restarted a thousand different times checking and unchecking the “reopen windows when logging back in” box. Basically I tried everything in the support community
What finally worked? I tried these last three together so I’m not sure which did the trick but I would try the easy Bluetooth remedy first.
1) Downgraded my WiFi drivers to the 10.6.4- there seems to be a problem with both Atheros and Broadcom chipset drivers- see directions here- http://thoughts.maayank.com/2011/08/wireless-problems-with-macbook-air-and.html
2) Turned on Bluetooth (I’ve always had it turned off)
3) Ordered a cheap USB Wifi stick (perhaps my Mac was shamed into finally working)
On an editorial note, I was fairly ****** with Apple never acknowledging they had a problem. Google “wifi no hardware found, mac” and you’ll get 8 million hits. Clearly there’s a problem. My family has 5 macs plus a few ipads, iphones, etc. Not that they’ll ever notice but I recently purchased a new phone. The choice came down to a iPhone or Droid. I went with the latter.