Make sure you have connected TV to the 2.4 band Wi-Fi network and also you can try changing channel for better connectivity. Please follow the steps mentioned on below article to change the Wi-Fi channel for 2.4 network. After changing Wi-Fi channel as recommended on the link restart the modem then we would request you to monitor the connection for next 24hrs.

http://arris.force.com/consumers/articles/General_FAQs/SBG10-Changing-the-Wi-Fi-Channel