Wondering since you said you have older Panasonic if maybe there was a video misconfiguration during setup. See if you can change your TV to 720p, unplug your HDMI, do the factory reset again (need to press and hold that button for at least 15 sec, I'd say 30). Make sure you are plugged into power outlet/wall not tv power for setup. (Also, make sure you are powered when doing the reset)
If you are able to get it to boot up again, select 720p when Display Settings Screen appears instead of Auto Detect or the like when prompted by Roku.
There is a chance you can access the Roku using some remote control debugging codes to do these things, but try the above first. You may not have held button in long enough for factory reset to occur.
https://support.roku.com/article/208757008 factory reset
See if that helps.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
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