Hi @dani-b,
Thanks for the post.
Try to hold down the reset button (it is located near where you would plug in the HDMI cables to the TV) for at least 30 seconds regardless of what happens on the screen and see if it helps.
If you are still unable to resolve the issue, we would recommend contacting TCL support to inquire further. Each Roku TV manufacturer provides direct support for their products running the Roku OS.
You can reach TCL here: TCL Support
Please keep us posted.
Regards,
Nimfa