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My Windows 7 got infected with a seriouly bad virus, just because I disabled my anti-virus, so after I re-enabled it I tryed to fight of viruses by doing a start-up scan, but my anti-virus froze and got disabled by the viruse, and all system files also got infected. So I re-installed Windows 7 and now I don't see the Ubuntu boot loader and I don't know what to do. I don't want to have to re-install Ubuntu too.

I'm new to linux, I don't even know what grub is.

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marked as duplicate by Alvar, Warren Hill, Basharat Sialvi, user68186, Tom Brossman Jul 17 '13 at 14:06

This question was marked as an exact duplicate of an existing question.

You can use the Ubuntu install media to boot and use fdisk to check the partition (ID is 83). Then mount it to /mnt and try installing grub to MBR. grub-install --root-directory=/mnt /dev/sda.

When it finished without error, reboot the system and you can see grub during start and can enter Ubuntu, but not Win7. After you enter Ubuntu, you can run sudo update-grub2 to update such as:

grub.cfg ...
Found Debian background: moreblue-orbit-grub.png
Found linux image: /boot/vmlinuz-2.6.31-15-generic
Found initrd image: /boot/initrd.img-2.6.31-15-generic
Found memtest86+ image: /boot/memtest86+.bin
Found Windows 7 (loader) on /dev/sda1
done
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