fdisk /dev/sda # Use 'a' to toggle active flag on the correct partition
# Mount root partition mount /dev/sda1 /mnt # Reinstall GRUB grub-install --root-directory=/mnt /dev/sda update-grub Using fdisk (Linux): active partition recovery full
bootrec /fixmbr # Rewrites MBR code (does not modify partition table) bootrec /fixboot # Writes new boot sector onto the system partition bootrec /rebuildbcd # Rebuilds Boot Configuration Database fdisk /dev/sda # Use 'a' to toggle active
From Windows PE command prompt: