Mine is now doing the same thing. Tv is literally 4 days old. Rescan can not detect any channels. Antenna hooked up to old tv works fine. I think its broke already. Onn 65 inch black friday special. It appears the tuner has quit in less than a week.
Can you please provide us the following information: -Roku TV brand and model -serial number -device ID -software OS/version (these can all be found in Settings > System > About) -tracker ID when this issue occurs (when you see this issue occur, press the Home button 5 times, followed by the Back button 5 times)
Once we have this information we will be able to assist you further.