Bootable USB stick doesn't get recognized by Computer

Hi all,
I have Ubuntu Desktop on a bootable USB stick that normally works, checked it on two computers, and its boots a-ok.
But on the third one, with a broken Ubuntu Server, it doesn't get recognized and doesn't show up on the Bios Boot Menu.

The computer displays Grub with no command working.

Any hints to what should I diagnose would be of greate appreciation. Thank you ( :