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