I was having trouble with my new installation on my rpi4. The issue was that it would boot and show the logo but then the screen went to black and I could not see anything. I could SSH in and my remote app showed it was connected.
It turned out to be the tv itself. The tv I am using is an older plasma tv that is only capable of 1080i (as opposed to the standard 1080p) the pi (or libreelec) apparently does not have the option for 1080i. I was able to work around this by booting with the HDMI in the port furthest from the power plug (though having the HDMI completely disconnected would likely work as well).
After booting connected the HDMI to the correct port and you should see the GUI with large grey bars on either side (without detecting a monitor it defaults to minimum resolution). From there I went to the setting and played with the setting till I found a compatible one (one of the 720 options). Other options had the grey bars or turned black again (it will revert to the old working resolution if you don't click the confirmation screen).
Newer tvs should not have this issue but older ones might. Hopefully this helps someone else.