I had the same issue with a 15' Macbook Pro (late 2008) and the OS X 10.8.5 update, and was unable to resolve it with any of the tips listed. I had to go back to 10.8.4 and all is working fine now. There seem to be numerous threads from owners of Macbooks and Macbook Pros from late 2008 and the 10.8.5 update. I'm sure many are hoping it's fixed soon.
Here's a typical thread of the many evolving on the Apple Discussion Boards on this issue:
Shutdown the Mac once. Wait 10 minutes. Reboot the machine. If that doesnt fix, it reset your SMC controller following steps here:
This has resolved a couple users issues in the other thread.
I have a fix!
just got off the phone with tier 2 apple tech support.
I have a mackbook 2008 and when I upgraded to 10.8.5 my wifi was completely broken.
Went through all of the typical reset PRAM, remove battery...etc.
Here is the fix:
Go to network prefs
remove the existing wifi configuration
select the - (minus sign) at the bottom left of the window.
Select Shut Down from the Apple menu.
Restart the computer.
Open Network prefs and select the + (Plus sign) at the bottom left of the window
For me, WIfi connection was populated already.
Go to the menu bar and you should now see all of your typical networks displayed.
Select your network.
Waallla! Sanity restored and your Macbook is back in action.
Have a great day!!