When installing Windows, it will never detect any other Operating Systems like Linux, Windows only sees Windows Operating Systems on the machine, nothing more. GRUB is a Linux boot loader, which helps to load Linux, or Dual-Boot between Linux and Windows. If you had Linux installed, and after installed Windows alongside Linux to use as Dual-Boot, it won’t work as Windows replaces GRUB with its own boot loader. To make it work, you will have to update-grub which will make it work. The tutorial is very simple and easy, follow the steps:
Boot from Live CD – find which Linux Distribution you are using, based on this boot from CD, and choose Try Linux, or on other versions Live Boot.
Find your main partition with GParted – Determine the partition number of your main partition. For example it can be /dev/sda2, but make sure you use the correct partition number for your system.
Mount your partition – use following command and make sure which partition you are mounting, in my case sd2 is correct: sudo mount /dev/sda2 /mnt
Bind mount – for i in /sys /proc /run /dev; do sudo mount –bind “$i” “/mnt$i”;
Chroot and Update Grub
sudo chroot /mnt
If it didn’t Work: Depending on your situation, GRUB sometimes cannot be fixed and you might have to reinstall it, if didn’t work try reinstal:
Now GRUB should work and you will be able to Dual-Boot between Windows and Linux.