Comment # 35 on bug 1175626 from John Shaw

With regard to my reply in comment 34, I do not get to the GRUB menu. If
SecureBoot is enabled, failure is an immediate blank screen(s) as the BIOS
exits POST. Nothing reboots the machine (eg, cntl-alt-del) other than
physically pressing the reboot button.

Other info: In my Asus BIOS, I can effectively disable SecureBoot by selecting
"Other OS" vs "Windows UEFI" under the SecureBoot section. This still displays
a line stating that SecureBoot is enabled, but the full linux boot sequence
works, and mokutil will confirm that it's disabled. I have read that clearing
the BIOS keys also disables SecureBoot, and that the BIOS will state so. I have
not tried that method.