Nothing happens when UBOS is supposed to be booting

/docs/users/faq-howto-troubleshooting/error-boot-fails/

Chances are, your boot stick or SD card (depending on the medium are you are trying to boot with) is bad, or writing the UBOS disk image to the card wasn’t successful.

This unfortunately happens. We recommend you write the image on the disk or stick again, and try again. If that fails, try a different boot stick or SD card.

Also make sure that your PC or other computer you used to write the boot image provided enough power to the boot disk or SD card during write; some do not, and this may lead to silently corrupted images.