First of all, I do not know the best answer to your question.
For a number of years I have played with Linux, Windows and boot managers. To date, the best tool I have founds Macrium Reflect.
https://www.macrium.com/reflectfreeThis program can make backup images as well as clone any partition. I can also create a legit boot CD to repair a PC that will no longer boot.
But it can not fix everything. That is why people have-to make backups.
GRUB may have overwritten the boot loader.
Do you have the Windows install DVD?