At times there may be one or two occasions where the network adapters such as AirPort or the Ethernet in your Mac suddenly cease to function properly, be that from hardware fault, software fault or accidental modification faults to your network. There is a way to reset them when things stop working as they should. If none of these methods work, you may have to send your machine in for some repairs if it’s hardware fault.
Resetting PRAM –
First steps, always try resetting SMC’s PRAM to see if that fixes the problem. Shutdown your computer and remove the power cable for atleast 15 minutes or so, I usually tend to do it in 7 to 8 minutes. If you’re doing it on Macbook or Macbook Pro, remove power cable and battery pack. Then you’ll plug them back in. Next hold down ⌘ + ⌥ + P + R as you turn it back on, You should know if it was successful as usually you’ll hear the startup sound twice.
Network Preference File –
If the above method didn’t work then try this, this may well guarantee a 100% proper fix. In guidance for this I’m using Mac OSX 10.6.8 Snow Leopard, newer systems like 10.7 Lion will most likely be the same. Older systems may well differ from what I’ll show you here.
Navigate to /Library/Preferences/SystemConfiguration in Finder (⌘ + ⇧ + G). You will find two files there which relates to your network. NetworkInterface.plist and Preferences.plist, you will want to rename them and give them the extension on the end with .bak, so it looks something like this;
You will have to change the current permissions temporarily for that folder so you can rename them just hit ⌘ + I to bring up information, then click on the Padlock and enter your password if it asks for one, next click on the + sign and add yourself into the group permissions and change it from Read Only to Read & Write then make your changes to those files. You can go ahead and leave the permissions for that folder or revert them back to their original state to Read Only for you then remove yourself by clicking on your name then click on the - sign. Next all you just have to do is Reboot and should be in working order hopefully, this method should reset and restore AirPort and Ethernet together.
When you’ve done your Reboot, the computer will automatically recreate those Plist files you edited and be in ready normal working conditions. I think it will be safe to delete the old Plist files after the computer has created the new ones, as you shouldn’t need it anymore.