Your TV should be switched on and out of standby mode. Press the 'Home' or 'Power' buttons to do so. This will help us to determine what you are seeing on screen.
Then follow these steps. Choose Help & Settings > Settings > Network > Change Network Settings > Connect to WiFi and follow the on-screen instructions.
Switch the power off at the socket. Wait 30 seconds before switching it on again. The TV box will then reboot which can take up to 10 minutes. Doing so can help the box to get signals from the WiFi Hub.