First you have to boot into Windows and disable hibernation and Fast Boot from within there.
To disable hibernation open command prompt as administrator and execute this command:
powercfg /h off
To disable Fast Boot open Control Panel go to Energy Settings, enable show hidden settings and uncheck Fast Boot. After these steps shutdown the machine (do NOT reboot) completely.
Then reinstall GRUB bootloader to your Ubuntu installation in EFI mode
Boot from the Ubuntu install media - then open a terminal and execute:
sudo mount /dev/sda8 /mnt
sudo mount /dev/sda2 /mnt/boot/efi
for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done
sudo chroot /mnt
grub-install /dev/sda
update-grub
Now you can choose which operating system you want to boot from the GRUB boot loader menu.
Note :
sda
= disk | sda2
= efi partition | sda8
= system partition
disk and partition numbers taken from your pastebin output
To get sure - check the partition numbers, you can easily identify them with GParted.
The (Graphic User Interface) tool is already included in the Ubuntu installation media.