If your ONN Roku TV is turning off by itself, there are several potential causes and troubleshooting steps you can try to resolve the issue:
Power source: Ensure that the TV is connected to a stable power source. Check if the power cord is securely plugged into both the TV and the power outlet. Consider using a different power outlet or power strip to rule out any issues with the current power source.

Remote control: Check if the remote control is causing the TV to turn off inadvertently. Remove any objects that might be obstructing the signal between the remote and the TV. Replace the batteries in the remote control to ensure they are not depleted or malfunctioning.

Sleep or power-saving settings: Verify the sleep or power-saving settings on your ONN Roku TV. Press the Home button on your remote control, navigate to Settings, select System, and then go to Power. Make sure the sleep timer is set to a suitable duration or disabled. Additionally, disable any power-saving features that may be turning off the TV automatically.

Software update: Ensure that your ONN Roku TV is running the latest software version. To check for updates, press the Home button on your remote control, go to Settings, select System, and then choose System update. Follow the on-screen instructions to update your TV if an update is available.

Factory reset: If the issue persists, you can try performing a factory reset on your ONN Roku TV. Please note that a factory reset will erase all your settings and personal preferences. To initiate a factory reset, press the Home button on your remote control, navigate to Settings, select System, and then choose Advanced system settings. From there, select Factory reset and follow the prompts to reset your TV.

If none of these steps resolve the problem and your ONN Roku TV continues to turn off by itself, it may indicate a hardware issue. In such cases, it's recommended to contact ONN or Roku customer support for further assistance or consider consulting a professional technician.