You wish to boot your Windows 8.x (or Windows 10) Stone Desktop PC or All-in-one (AiO) machine using the in-built legacy PXE option firmware so that you may connect to your existing bootable network infrastructure for the purposes of operating system deployment.
You system has been supplied to you from Stone with Windows 8 or above and when you attempt to to use PXE boot you are unable to find the boot device in the F8 boot menu or in the boot device priority list within the system BIOS.
Windows 8.x (and 10) based machines must be shipped from the manufacturer with a BIOS feature called 'Secure Boot' enabled. This feature is intended to ensure that only authorised software can be booted on the host system
When Secure Boot is activated on a PC, the PC checks each piece of software, including the Option ROMs and the operating system, against databases of known-good signatures maintained in the firmware. If each piece of software is valid, the firmware runs the software and the operating system. This restricts the use of the Legacy PXE option ROM.