What model Roku do you have? Model number, not name, please. How are you powering the Roku (USB port on the TV or the wall block power)? Do you see the dancing Roku logo when you first power it on, or does the screen ever show anything? Note that the TV must be already turned on and set to the correct HDMI port before you power up the Roku to see the Roku boot screen.
Dan
Roku Community Streaming Expert
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