Does the issue only occur on a specific channel or across other channels installed on your Roku? Are you using a Roku TV or a Roku device connected to a TV? Please reply here with your device model number which can be found in Settings > System > About. I'll be able to further assist you from there.
This had happened to us as well. You can’t see anything. It’s only Audio. You can’t see the Home Screen let alone get to settings. We shined a light on the screen and you can kind of see the Roku name. But like i said, screens black only sound.