After Windows reinstall the windows would overwrite the GRUB. If using Ubuntu 9.10 or later or have the GRUB2 installed then see here - 1. https://help.ubuntu.com/community/Grub2 2. https://help.ubuntu.com/community/DualBoot/Grub If using older GRUB legacy version then the situation is a little bit tricky but not hard. There are two ways to do this. A) Use older LiveCD, possibly of Jaunty. 1. Make a bootable USB. Use unetbootin and not the Startup disk creator otherwise you will have the error vesamenu.c32: not a com32r image ( https://bugs.launchpad.net/ubuntu/+source/usb-creator/+bug/686041 ) 2. Boot into LiveCD. 3. Run grub sudo grub 4. Find where Grub is. grub> find /boot/grub/stage1 (hd0,5) This may or may not be the correct partition where grub resides. If there is /boot partition in addition to a root partition then there might two locations where grub is installed for e.g. /dev/sda5/boot/grub and /dev/sda6/boot/grub. The one that contains the menu.lst is the one that is ...