I would suggest connecting something else to the TV, such as an antenna or DVD player and see if the TV still does that. That would lead me to believe that it is the TV if it does it with something else connected. A Roku 2 is also extremely old, technologically speaking, and is at the age where it will start having issues with compatibility as well, but I would test the TV too as a TV 15 years old, the screen could be going out.
