Sounds like the backlight might be out. I suggest contacting customer support for warranty service/technical support. If it is a Roku brand, go to the Roku customer support page and scroll down to agent support.
If another brand, you would need to contact that manufacturer (Onn, Hisense, TCL, etc...)
Hey there, @MomsTV50.
Thanks for sharing this here!
Looks like your Roku Plus Series TV's screen went black, but you can still hear sound. We'd like to check it out a bit more.
To further assist you, please keep an eye on your inbox as we have sent you a private message.
Looking forward to your response from there!
Best,
The Roku Community Team
Manufacturer support contacts for Roku TVs from Roku and other manufacturers can be found in this support page: https://support.roku.com/article/115006475047