i previously had windows 7 and ubuntu 13.04 dual boot ..working perfectly.. then i did a clean installation of windows 8 over my win7 partition..it succeeded .(by disabling the Uefi option in bios) then i tried boot-repair x64 disk of ubuntu to repair ..but it didnt installed grub .. moreover grub options in the advanced tab (of the repair disk utility) are disabled how can i force install grub on sda..or any other way
Installing Grub manually is fairly simple, and once you get it, there shouldn't be anything keeping you from dual-booting successfully.
First, boot the computer up off of your standard Ubuntu installation disk. You should be using the same version (e.g. 13.04) and the same architechture (e.g. amd64, 64-Bit) as your currently installed Ubuntu. If you need to download an old version, you can do so at http://releases.ubuntu.com.
Once you've booted the disk up, press Ctrl+Alt+T to open a terminal window. In that, type in the following commands:
sudo mount -t ext4 /dev/sda1 /mnt sudo mount --bind /dev /mnt/dev sudo mount --bind /proc /mnt/proc sudo cp /etc/resolv.conf /mnt/etc/resolve.conf
Note that that last command may fail if you aren't connected to the network. It isn't strictly necessary, so if running it gives you an error, you can simply ignore it.
Also, you may need to replace
/dev/sda1 with something else, depending on the hard disk partition you have Ubuntu installed on. You can get help with determining the exact line in This Question.
Once you've done all of that, we're ready to proceed. In the terminal, enter in this command:
sudo chroot /mnt
You'll see the prompt in the terminal change from
ubuntu@ubuntu:~$ to something like
root@ubuntu:~#. It may be different for your specific machine. This tells us we're ready to install grub. Run this command to do it:
grub-install --force /dev/sda
Once you're finished with this, reboot your computer. It should boot back up into Ubuntu.
Next we need to add an entry for Windows 8 into Grub, and remove any Windows 7 entries that are still there. To do this, open another terminal window, then enter this command:
This command will take a minute or two, then you're all set. If you reboot your computer, you should be prompted to boot either Ubuntu or Windows 8.