Try resetting your internet connection (unplug/replug modem or router). Alternatively, try resetting your DNS.
Power off your modem/router for 5 minutes, turn it back on and then perform this command.
Windows XP:
- Click Start and then Run
- Type cmd in the run box and click Ok
- In the Command Console window that has appeared type: ipconfig /flushdns
- After typing the above command, press Enter to execute it and then close the window
Windows Vista / 7:
- Click Start, then Programs, then Accessories and then locate 'Command Prompt'
- Right-click on 'Command Prompt' and left-click on 'Run as Administrator'
- In the Command Console window that has appeared type: ipconfig /flushdns
- After typing the above command, press Enter to execute it and then close the window
If that doesn't work, clear the cache or cut and paste your interface folder onto your desktop and launch WoW.