To fix it try several things:
1.
Reset Your PRAM and see if that helps.
2. In OS X go to System Preferences->Network tab and at the top of the Network tab will be the 'Location' toggle-bar. Use that to 'Edit' (in 10.8.x) Networks and then in the pop-up use the + button to add a custom named Location, then save everything when prompted to save this change.
Don't worry, this Network Location change will act the same as 'Automatic'.
3. Also in the System Preferences->Network pane click on the 'Advanced' button. In the drop-down click on the 'DNS' mini-tab and put in free DNS servers from either
OpenDNS.com or
Google's free DNS. See if that works.
Good Luck.