"GPT detected. Please create a BIOS-Boot partition" while using boot-repair

Since I updated Windows to 8.1 my Grub menu disappeared. I ran Ubuntu using Live USB, I used Boot-Repair but something went wrong. If I click on Reccomended repair I get this error:

GPT detected. Please create a BIOS-Boot partition (>1MB, unformatted filesystem, bios_grub flag). This can be performed via tools such as Gparted. Then try again. Alternatively, you can retry after activating the [Separate /boot/efi partition:] option.

So I tried to set my sda9 (I think that it's the Ubuntu system partition, since it's ext4) with the bios_grub flag and then to run Boot-Repair again. It didn't work.

I don't know what to do. My Grub was working fine (using UEFI) before I updated Windows.

I removed the bios_grub flag. Then I used fsck and it didn't find any error. So I tried again with Boot-Repair but it always gives me the "GPT detected" error. My boot is on UEFI mode, Secure Boot is "off".

When I boot my PC with SecureBoot OFF, I can reach the GRUB menu. But it's empty (the only voice is "System Setup").

I mounted my Ubuntu system disk:

sudo mount /dev/sda9 /mnt

and the other things:

sudo mount --bind /dev /mnt/devsudo mount --bind /proc /mnt/procsudo mount --bind /sys /mnt/sys

I logged on the system with chroot:

sudo chroot /mnt

I re-installed grub:

grub-install /dev/sdaupdate-grub2

But it still doesn't work.