This from Lenovo:
While the "To interrupt normal startup, press Enter" message is displayed at the lower-left area of the screen, press the F1 key. The BIOS Setup Utility menu will be displayed. If a password prompt appears, type the correct password.
Do not know how your got grub legacy installed to MBR, but you only have UEFI boot and data in MBR will never be used.
Many vendors now modify UEFI to only boot Windows by description. So ubuntu entry does not work. But UEFI also boots hard drive entry as /EFI/Boot/bootx64.efi. So we copy grub into /EFI/Boot and rename it ot bootx64.efi and system will boot from hard drive entry.
From live installer mount the efi partition on hard drive
Mount efi partition. check which partition is FAT32 with boot flag. Often sda1 or sda2 but varies.
sudo mount /dev/sda1 /mnt
mkdir only if not already existing, your have this but others may not:
sudo mkdir /mnt/EFI/Boot
sudo cp /mnt/EFI/ubuntu/* /mnt/EFI/Boot
If new folder created, the bootx64.efi will not exist, skip this command
sudo mv /mnt/EFI/Boot/bootx64.efi /mnt/EFI/Boot/bootx64.efi.backup
make grub be hard drive boot entry in UEFI. If not existing, may have to update UEFI also with efibootmgr.
sudo mv /mnt/EFI/Boot/grubx64.efi /mnt/EFI/Boot/bootx64.efi
Other work arounds:
Dual boot Win 8 / Ubuntu loads only Win
windows 8.1 changes boot order
How do I get my HP laptop to boot into grub from my new efi file?
Best Answer
Access boot priority menu
The boot priority settings are often found under the Boot tab of the computer's BIOS/UEFI utility. The BIOS/UEFI utility can be accessed by pressing the key which is shown on the manufacturer's splash screen when booting. This is the F12 key on many computers. The keys to press, such as F12, F2, Del or Esc, differ on computers from different manufacturers. When grub bootloader is installed it does not change the key which is used to access the BIOS/UEFI utility.
There is a table of keys used to access the BIOS/UEFI setup utility grouped by manufacturer and computer model at this answer.
Access GRUB menu
Immediately after the BIOS/UEFI splash screen during boot, with BIOS, quickly press and hold the Shift key, which will bring up a GNU GRUB menu screen. With UEFI press (perhaps several times) the Esc key to get to the GNU GRUB menu screen. Sometimes the manufacturer's splash screen is a part of the Windows bootloader, so when you power up the machine it goes straight to the GNU GRUB menu screen, and then pressing Shift is unnecessary.