Grub 2 typically gets overridden when you install Windows or another Operating System. To make Linux control the boot process, you need Reinstall (Repair/Restore) Grub using a Linux Live CD.
ROOT_DISK='/dev/sda2' BOOT_DISK='/dev/sda1' # optional, only for EFI DISK='/dev/sda' mount $ROOT_DISK /mnt mount $BOOT_DISK /mnt/boot/efi # optional for i in /dev /dev/pts /proc /sys /sys/firmware/efi/efivars /run; do sudo mount -B $i /mnt$i; done chroot /mnt grub-install $DISK update-grub # don't forget to update UUID in /mnt/etc/fstab using blkid