you only need either the HDMI or the rca cables, not both. I would use the HDMI cable from the cable box to the TV. Then on the TV remote there is probably an input button. Select HDMI. Make sure to pick the right HDMI 1-4 that you plugged into. It might only show the inputs you have connected. I'm looking at the manual right now. Doesn't look like your remote has a separate input button. It's probably under Q Menu.