Based on (limited) information provided I'm guessing your display or HDMI cable is faulty and isn't providing an EDID.
This thread may be helpful:
Thread
older tv without 1080p
I have an older TV that does not support 1080p. I can't seem to get any picture on it. Initially I tried connecting my already built libreelec box on a RPi 3, but the TV displayed an error message. I then tried doing a fresh libreelec install v11 (maybe I should try v10?). Same result. I see the initial rainbow splash screen, but then the screen goes black and the TV eventually displays an error message that it can not display the picture.
I tried forcing 720p using config.txt and…
I tried forcing 720p using config.txt and…
mikeybs