"Had the same problem with my mid 2009 Macbook Pro 13 inch running Mountain Lion. Temporarily (appears to have worked, issue may return in a few days, hopefully not) fixed it by doing this:
1. Make sure ""restart programs"" when logging in is NOT checked. See here: http://macnerd-presents.blogspot.com/201...
2. Rebooted and held down ""command + s"" to go into single user mode and run /sbin/fsck -fy and if you see ""disk modified"" at the end, run again until you see ""your disk is ok"" For more info see here: http://support.apple.com/kb/ts1417
3. Reboot and log in and see if the wifi is showing ok. If not, go into System Preferences and Network and add a new wifi connection using the default naming conventions. See here for more info: http://www.chriswrites.com/2012/05/how-t...
"As a workaround you can use a USB wireless dongle (just be certain the one you buy supports use on a Mac or you'll have driver problems). It is also possible to purchase a USB ethernet cable dongle (if you can work at a place that has a hard cable connection) while you're waiting for your part to arrive.
If this Answer is helpful please remember to return and mark it Accepted."
"This happened to me on my 2009 MacBook Pro, I tried all the software fixes to no avail.
No WiFi Hardware Installed, Very frustrating, If you have a range of screwdrivers available and wish to
I decided to open up my MacBook Pro and investigate myself, if the problem was related to the Airport card,
On inspection after removing the screen to get to the area where the Wi-Fi card is housed, underneath the black plastic clutch cover, I simply resitted the cable where it connects to the WiFi card, I then had to re connect the airport card cable on the motherboard and the display connector and battery , before putting it all back together, I then powered up the laptop and instantly I had WiFi again.
There is a excellent video tutorial available on youtube:
