A:Answer First, check your input button on your remote and make sure it matches whatever it is you're linked through (Roku box, DVD, etc.). If that's not it, try turning the TV on and off and using the TV input on your remote, and then follow the instructions onscreen for setting up through your cable or roof-top antenna.
If you are using an HDMI cable, try changing to another cable to make sure the HDMI cable is not malfunctioning.
That will work 99% of the time. If it's not that, you may simply have gotten a bad TV...which is rare but possible.