Is it a TV made by Roku or another manufacturer (TCL, onn, Hisense, etc.)?
How to know if you have a Roku TV or a Roku-branded TV | Official Roku Support
Can you see any picture at all? Try shining a bright light on it.
You may as well try a factory reset:
How do I factory reset my Roku® streaming device? | Official Roku Support
It should still be under warranty, but if the TV isn't made by Roku you'll have to contact the manufacturer:
Where can I get support for my Roku TV™? | Official Roku Support
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