Test your hardware first then to eliminate that.
Is the HD detected in BIOS setup? If so test it. If not reinstall it or replace it.
Try resetting the BIOS to defaults: Clear CMOS - 3 Ways to Clear the CMOS - Reset BIOS
Is the disk you're trying to boot known to work? If not try it in another machine. There are several disks needed in the tutorial so also try another one. What happens with Windows Defender? You can also write it to stick.
Try unplugging the HD to see if disk will boot. If this fails, try flash stick boot. If it fails try unplugging the DVD drive. The tool to write the installer to flash stick is in tutorial.