There is a URL link to debugging with a serial console. Is it possible for you to get a serial console boot log?
Sadly, on first boot there is no admin account until you set this up. Serial console does offer an alternative to completing this when there is no HDMI (or HDMI is failing), so this is useful for more reasons than just logging (serial console is the only way to log boot stages prior to Linux, so it has extreme utility).
If the first boot had been set up, then you could also try ssh. Alternatively, one could get past GUI/graphical mode and try text mode with key combination “CTRL-ALT-F2”, but if no account is set up, then you couldn’t use this even if it works.
I wouldn’t advise it, but you could create a first boot setup from the host PC so that it isn’t needed on the Jetson itself (even the first boot would act as if the setup were already complete). One reason I don’t suggest it is that if something else is wrong, then you wouldn’t get to login anyway. And if the graphical mode is the issue, then it’ll still be an issue, so you’d be back to using serial console (I do highly advise getting a cheap serial UART cable for serial console…it is invaluable for much in the embedded world). However, see this if you want to flash with first boot already set up:
https://forums.developer.nvidia.com/t/jetson-nano-all-usb-ports-suddenly-stopped-working/75784/37