Hi Charlie,
Sabya here, Independent Windows Adviser. Hope you are doing well.
This message is generally displayed when the output resolution of the device is not supported by the TV. Can you please let me know what did you change?
If you have changed the TV then the resolution that was provided by your xbox does not match with the TV.
If you have any other display try plugging your xbox to that device and try to change the resolution of your xbox to match the tv