On a number of occasions, I've opened my MacBook Pro (OS X 10.5.8) quickly and tried to use the internet before AirPort could connect to my usual network. Sometimes this causes the AirPort to get "stuck" in a weird state, where you can no longer use that network. Even rebooting the MacBook doesn't help.
Looking at System Preferences → Network → Advanced → TCP/IP you could see that IPv4 was something like 168.254.x.x and the Subnet was 255.255.0.0. This is the IP address that Mac assigns itself in the case when it failed to get an IP from the DHCP server. (You might also try turning off your firewall. Here's more info.)
Here's what I've done to fix it:
- Turn the AirPort off (under System Preferences → Network)
- Open the Terminal App.
- type sudo rm /Library/Preferences/SystemConfiguration/com.apple.network.identification.plist and hit ENTER. (You will need to type your password.)
- type sudo rm /Library/Preferences/SystemConfiguration/com.apple.airport.preferences.plist and hit ENTER
- restart your MacBook
- Turn the AirPort on.
Those plist files will get regenerated, and your wireless passwords are even remembered! (blog comments powered by Disqus