Long shot....
Roku has a secret menu to stop the Roku from trying to reset it's resolution each time. Which can result in no image.

"Re: Stop Roku Ultra from Changing Resolution back to Auto Detect
The Roku will switch back to autodetect if it believes that the tv has changed and it doesn't support the current manual setting. In order to prevent the dreaded black-screen/invalid video format it resets back to auto-detect."

Deactivate Auto:
Press Home 5 times, Down, Left, Up 3 times

Other secret menus:
[Link: lifehacker.com]