|Even if the Boot Order or similar is set correctly, with the network boot after hard drive in the list, if there is no hard drive and if there is no bootable optical disk inserted, the bios will attempt to boot from a network.|
Or - for some laptop bioses, if there is a hard drive but there is no operating system on it and if there is no bootable optical disk inserted, the bios will attempt to boot from a network.
Usually you can't remove the network boot from the list - you can only change where it is in the list. .
If you install a hard drive AND install an operating system on the hard drive, then the bios will boot from the hard drive rather than attempting to boot from a network.
In order for you to be able to boot from a bootable optical disk, CD drive or similar does not necessarily need to be first in the Boot Order or similar list - it just needs to be before hard drive or similar,
In many bioses, floppy drive or removable drive must be before CD drive or similar, otherwise a bootable floppy disk in a conventional floppy drive or a USB floppy drive will not be recognized as bootable by the bios,
This boot order does not need to be changed when you change which source you're trying to boot from.
Floppy drive, or removable drive