Macbook air 13" 2008

Hi I have owned my macbook air for a couple of days and have been using the internet via my home wi fi perfectly fine. Today i installed itunes and restarted my mac the internet would not work so i entered my internet WPA again and it keeps saying "connection timeout"

Someone suggested to try

Open System Preferences, Click on Network, Select your WiFi on the left and click the Advanced button at the bottom, click the TCP/IP tab and click the Renew DHCP Lease button. Click OK.

Try it again.

but its still not working :/

mmm not sure what´s going on there. i don't think that itunes is the problem. do you have other devices connected such as a playstation (to the network i mean) that can definitely cause trouble.

Turn off Airport (wifi), then open network prefs>Advanced, delete your network from the list, then Apply. Then open keychain utility (in utilities folder), search for all instances of your network and delete them. Then rejoin the network from fresh.