I had Arch linux on my computer and needed Windows for gaming; Windows installs its own boot loader, so I had to re-install grub. The following is what I did to restore grub.
I suppose that you know what you're doing! For example you need to know in which partition linux is installed.
Boot Arch linux from live CD.
Create a directory for chroot environment:
mkdir /mnt/root Mount the root partition and other necessary device and file systems:
