Jetson Xavier NX Dev Kit will not boot

I was working on installing Cuda toolkit and OpenCV with Cuda support and was prompted to restart my Xavier. I did so and when it tried to turn back on, the white screen with the Nvidia Logo showed up, then it went black and continued to alternate between no video output and just a black screen. I have put a different sd card from another one of my jetsons into the board and it still works so I know it is not a hardware issue. When I put the other sd card back in, the same thing happens as before. Any ideas of what could have happened / how I can fix it, or at least get a backup of my system so I don’t lose all of my work?

I couldn’t tell you any specific place or reason, but you might poke around in the log files with the SD card partition mounted on your host PC. Logs would be in “/var/log”, and the “syslog” (or older ones with number) might offer a clue. If packages were changed, then logs in the dpkg logs would likely help. The apport logs would possibly tell you about an app crash. Note that they should all have timestamps, and you could ignore anything that isn’t from the correct date.

Also, if you watch serial console and log this during boot, then it would help because it might actually point out the problem directly.

sometimes if disk space exhausted it might have such sympthoms [like no space left]

+1 for @Andrey1984’s idea. Hadn’t thought of that, but when the rootfs of the non-working SD card is mounted on a host PC, how full is it? If for example you’ve mounted this on “/mnt”, then what do you see from “df -H /mnt”?