You can try to repair GRUB.

1. To do this, boot from any Live CD and open a terminal.



2. Mount the partition with your installed Ubuntu by entering

   
   
   

   sudo mount /dev/sda? /mnt
   
   

   
   
   

   Important: replace the '?' with the partition where you installed Ubuntu!
   If you don't know which partition this is, open gparted and look for it.




3. Include the directory with important device information

   
   
   

   sudo mount -o bind /dev /mnt/dev 
   
   

   
   
   

   and /sys

   
   
   

   sudo mount -o bind /sys /mnt/sys 
   
   

   
   
   

   and the interface data

   
   
   

   sudo mount -t proc /proc /mnt/proc 
   
   




4. Now change into the mounted system:

   
   
   

   sudo chroot /mnt /bin/bash
   
   




5. Then you can install GRUB by typing

   
   
   

   grub-install /dev/sda
   
   

   
   
   

   and

   
   
   

   update-grub
   
   

   
   
   

   If you get Errors with the last step, just mention it in a comment.




6. Exit the terminal with exit.

Hope this is helpful for you.