Warmest welcome here in the Roku Community, @cootie!
It is highly appreciated that you've reached out to us about setting up your new Roku Express 4K and we'd be more than happy to be of assistance.
Have you also tried to set up the HDMI input using the remote of your TV? In addition, can we please try to connect/plug your Roku Express 4K to a different TV to see if this will make any difference? (Please make sure that if you've plugged it into a different HDMI port, please don't forget to set up the correct HDMI input using the remote of your TV as well.)
Let us know how it goes and we'll continue assisting you from there. Hope this helps!
Best regards,
Carly
Carly Y.
Roku Community Moderator