I rebooted many times with known-good USB flash drives in different ports. When I get to the boot choice (hit Esc at BIOS splash screen, follow prompt OR just F9 at BIOS splash screen) I see the internal hard drive, a blank but selectable line, then CD/DVD drive.
I've gone into the BIOS and there's no secure boot option or anything but I can get into the boot order and the USB flash drive shows up there.
rufus
sooftware? Also you need to change theUEFI
in the bios option, but be aware of that you may can't access your old operation system anymore.