I have a raspberry PI 4b, with an case that came with the system.
I am trying to boot with the hdmi screen, and usb keyboard, plugged into a switch. The screen turn on when the rpi boots, but within 5 seconds the monitor reports no signal.
I have changes some settings in the SD card boot partition, confit.txt:
hdmi_safe
hdmi_group
hdmi_mode
config_hdmi_boost
nothing appears to work, same problem.
The ethernet interface does not appear to be enabled either, nmap does not find the host (other than my desktop & the adsl modem/switch)
The system boots fine with an ubuntu image.
I have also tried to check log files (/var/log/*) in the rootfs partition of the sd card. but there doesnt appear to be anything relevant there (no kern.log?).
Any help appreciated
Edit: This was a power supply issue.