Boot – Understanding Safe Graphics Mode

Solved I reinstalled in UEFI mode and now it boots into my OS as it should. The issue was cause by initially installing in legacy BIOS by mistake.

It's not clear if you've installed Ubuntu in BIOS/CSM/legacy mode or if you're saying you haven't yet installed it but that you can boot the installer in BIOS mode.

If you want to boot the installer, either to install directly or to run Boot Repair, you must find your EFI's built-in boot manager. In most cases, this can be accessed by hitting a function key early in the boot process, but which one is completely non-standardized. (Some computers also use some other key, like Esc.) When it comes up, it will usually have two options for external media, one of which includes the string "UEFI" and the other of which does not. Select the "UEFI" option to boot in that mode and the other one to boot in BIOS/CSM/legacy mode.

In some cases, you may need to enter the firmware setup utility to disable its "fast start" feature (or words to that effect; again there's no standardization) in order for the boot manager to become available.

Also, note that only the 64-bit version of Ubuntu has an EFI boot loader. The 32-bit (x86) version lacks an EFI boot loader and so is not bootable in EFI mode unless you add an EFI boot loader of your own -- and installing the 32-bit Ubuntu on a system with a 64-bit EFI adds another layer of trickiness, so I do not recommend going that route.

Secure Boot should not be an issue, but sometimes it is, so disabling Secure Boot may be worth doing if you try other things and still can't get it to work.

As a general rule, you should not perform a BIOS/CSM/legacy-mode install of Ubuntu on a computer that already has Windows booting in EFI/UEFI mode. If you've already installed in this way, you pretty much must get the Ubuntu installer booted again in EFI mode, either to run Boot Repair or to re-install Ubuntu. The other option is to install an EFI boot loader in some other way. For instance, you could use the USB flash drive version of my rEFInd boot manager to boot Ubuntu in EFI mode, then either switch from the BIOS-mode GRUB (grub-pc) to EFI-mode GRUB (grub-efi) or install rEFInd to the hard disk via the Debian package or PPA.