Make sure a security management password is set, so to enable several of the functions, and that Secure Boot is enabled (initially, for same reason) in the Boot tab.
One therefore needs to fiddle in the UEFI (BIOS) configuration to make an Ubuntu-only installation bootable:
But after installing Ubuntu and formatting the HDD in the process, an error appeared at boot-up: 'Default Boot Device Missing or Boot Failed', or 'No Bootable Device', probably once the UEFI/BIOS has been cleared. I first had dual-boot for a couple of years, but then wanted to delete Windows and recover that partition. Further to Piyush, this is also how I solved this problem on my Acer Aspire e5 575.
