My Mac does not connect to the Internet. Webpages do not open in Safari or other web browsers. These pages may be blank or you may receive an alert that You are not connected to the Internet. Internet applications such as Mail, iChat or the App Store cannot connect to their servers.
Have there been any changes in the WiFi configuration? When you are asked for the password make sure to select the proper security option (WEP WPA WPA2 "¦).
If there are multiple devices on your WiFi/network make sure the DHCP range is large enough to provide all devices with internal IP addresses. One often loses track with all the mobile phones tablets etc. connected to a network nowadays.
In System Preferences > Network select your AirPort adapter click the advanced options and remove the network from the preferred network list so no old saved settings override the required ones.
Finally wipe all the AirPort and NIC settings off your Mac "“ go to /Library/Preferences/System Configuration/ and delete the following preferences lists com.apple.airport.preferences.plist com.apple.network.identification.plist NetworkInterfaces.plist Followed by a reboot.
You may lose certain settings by doing this. You will lose saved networks. You may have to go into System Preferences > Network click the Add (+) button and add your AirPort NIC manually afterwards.
Alternatively you can open up a Terminal window and input "/usr/sbin/networksetup -detectnewhardware".
You need to be in /Library/Preferences and not ~/Library/Preferences .. with finder active select the go menu and choose go to folder"¦ type in /Library/Preferences/SystemConfiguration and you will see the files"¦
It will require an administrator password to delete them and if you move them to somewhere besides trash it just going to copy them instead of moving them.