Short version Cannot restore EFI partition with boot repair. Create a proper partition AND put a /EFI/ folder into it, then used boot repair
I originally had a dual boot with win 8 on it. Deleting it also bricked my EFI boot partition. I eventually reinstalled Ubuntu 14.04 via a live USB as my kernel images were ruined by boot-repair, hoping this would also fix the boot, but that didn't work.
My current partition status:
where sda3 is the former windows partition, and sda6 contains data (backed up). sda2 holds my ubuntu install.
edit I removed sda1 and placed the bios_grub flagged partition at the start of the disk, reinstalled grub and updated, but to no avail /edit
My current boot status is given here:
Despite this, if I boot without my live usb in, I only get a black (non grub) screen stating that all boot option have been tried.
I can manually boot the sda2 ubuntu by running grub from the usb key in UEFI mode, pressing c to get the CLI interface, and using
grub> linux (hd1,gpt2)/vmlinuz root=/dev/sda2 grub> initrd (hd1,gpt2)/initrd.img grub> boot
Then, I tried both using boot-repair and installing grub manually by
sudo grub-install /dev/sda sudo update-grub
both end up fine with no errors, but I still get the black screen.
Also, I am unable to boot the system manually if a run my grub on the usb key in non UEFI mode, since I cannot reach the Command Line Interface in this case (holding shift leads to a crappy grub GUI and I am stuck there).