First I'd unplug power from the box for 2 minutes or so then power it up and let it reload. After that check all your coax connections, make sure they are tight. You can also go into menu> customer support >Top support tools>Connected device status and make sure connections show good connections. Also you can try menu> customer support >Top support tools>Reboot STB. You might also try a different HDMI cable from box to tv.
