H47IU

        Result is important.
        If the procedure is correct with no result,
        then some part of the procedure is still hidden..

Life in a Sandbox I of III
--------------------------

I. CHROOT. restore grub in a doubleBoot (Windows 10/Linux) computer
...................................................................

  Use doubleboot.vhd virtual machine.

a. Destroy grub

Boot from en_windows_10_pro_15063.0_x64_dvd.iso
Choose "Repair your computer"

  Troubleshoot ->  Advanced options -> Command Prompt.
  
  > Bootrec /fixMbr
  > Bootrec /fixBoot

  Restore -> Advanced -> Command prompt
  
    x:> d:
    d:> bootrec RebuildBCD
    d:> bootrec Mbr
    d:> bootrec fixboot
    
Close CLI. Reboot from HD. No Grub, no boot into Linux.

b. Restore grub

Boot from systemrescuecd-x86-4.9.5.iso

  % fdisk -l /dev/sda
  % mkdir /mnt/linux
  % mount /dev/sda2 /mnt/linux
  % mount -o bind /proc /mnt/linux/proc
  % mount -o bind /dev /mnt/linux/dev
  % mount -o bind /sys /mnt/linux/sys
  
  % chroot /mnt/linux /bin/bash
  
  % grub-install /dev/sda
  % update-grub
  % exit
  
Reboot and enjoy Grub is back.

Viited
......

1. Google: windows 10 restore bootloader

     http://pureinfotech.com/repair-master-boot-record-mbr-windows-10/
     
2. Google: systemresque restore grub

     http://www.system-rescue-cd.org/disk-partitioning
          /Repairing-a-damaged-Grub/