I'm having a similar problem with my Roku Stick+. It will no longer interface with my TV. I receive an Invalid Mode error on my TV. It appears that the Roku Stick has changed the HDMI port resolution to 0, 0 and I can't get it to change to anything else.
Thanks for the suggestion. I was able to reset and enter the setup menu. When it got to the autodetect of the HDMI port, everything checked out. However, when it entered automatic mode, the screen went to "Invalid Mode". This indicates to me that it is trying to tell the TV to change to an unsupported resolution.
It will not display at 1080p. I can only get it to set up at 720p.