No offense but it would help if people providing answers had some vague knowledge of how electronics actually work. It's not just some random "maybe it works maybe it doesn't" topic, and nobody needs religious blessings to fix their TV.
Roku TV's are made by many different manufacturers. They aren't made by Roku. I have one made by TCL. There are various "hard reset" procedures depending on the manufacturer. Obviously the power button is in different places depending which brand and model you have.
Most hard reset procedures involve some variation of holding down the power button in combination with other buttons while turning on the TV.
If a hard reset doesn't work, you have defective hardware in your TV -- the operating system on the motherboard isn't functioning correctly.
I would strongly recommend against buying replacement parts for TV's unless you are an expert on troubleshooting electronics. A failed motherboard could just be the result of a bad component elsewhere and the cost of these parts will quickly surpass the cost of a new TV. Circuits are an interconnected system, the signal flows like water -- a problem in the power supply can manifest itself somewhere physically distant in the circuitry.
