Boot from DVD

I installed windows 10 for testing without any problem. Booted from DVD and so far has been rock solid, idling 2-5 watts measured from the wall. I'd like to test out some firewall distorts, and here is where my problems begin. I can't for the life of me work out how to boot from DVD like it did on the first day. There is no option to boot from DVD in the bios. My DVD player is recognised as a 'mass storage device' but there is no option in the boot menu to select it as a priority. Is this something to do with secure boot? And if so, how can I turn it off?