I have a Pi 3. It works fine some days on monitors (DVI 4:3 and HDMI 16:9) and TV (HDMI 16:9).
Now, monitors get "No video input" but TV still works.
I switch the Pi 3 with a friend Pi 3 (same SD, same cables, same monitors) and it works.
I seems my Pi 3 is broken for monitors (DMT mode).
I try a lot of configuration on /boot/config.txt without any success.
There is a kind of "bios" to reset, because it cannot be a software on SD issue (works with an another Pi 3).