Do you have another tv you can try this on? If it works there, try setting Settings > Display type to the actual resolution of the first tv, not the "auto" setting. If you see a countdown screen click on the Yes button. Now try it back on the original tv.
If no other tv, try a different HDMI port if there is one.
- Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
- Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T
- TCL Roku TV 43S425/C107X, Ser X000001R60KV, wifi