I have no possibility of accessing the BIOS on one of my machines--no screen (the system is hopelessly buried behind other equipment) and no one to read it even if I had one. This system booted from its DVD drive at one time, but now no longer does, and I don't know why. I can mount the DVD with the command: mount -t 9660 -o ro cdrom and show the filesystem with df, but if I reboot the system with the reboot command or turn it on from cold, seems like the DVD drive gets bypassed. I have also tried booting the system from a USB thumb drive suitably prepaired with Debian 11.6 by writing it with IMGBurn, and still no joy no matter which USB port I choose. Is there a way to force the CD/DVD drive to boot from maybe an installed boot manager package that I can install on my Debian 8 system so as to boot the Debian 11 DVD and regenerate my system?