It sounds like you tried something like this already, but I don't know exactly what you tried, so I'll post it anyway. Pay attention to the X and Y and make sure you get them right. I have used this method many times and it has always worked, but please forgive me if this is what you already tried.
This is a quick and simple method of restoring a broken system's GRUB 2 files. The terminal is used for entering commands and you must know the device name/partition of the installed system (sda1, sdb5, etc). The problem partition is located and mounted from the LiveCD. The files are then copied from the LiveCD libraries to the proper locations and MBR. If, for example Windows is on sda1 and Ubuntu is on sda5, and Windows has overwritten the MBR, then the target for grub installation will be /dev/sda5, and the MBR in the boot sector of sda will be re-written for grub.
This operation will write to the MBR and restore the modules and core.img to /boot/grub. It will not replace or restore grub.cfg or fix corrupted files.
Boot the LiveCD Desktop.
Open a terminal window.
Determine the partition with the Ubuntu installation. The fdisk option "-l" is a lowercase "L".
sudo fdisk -l
If you're not sure of the partition, look for one of the appropriate size or formatting.
Running sudo blkid may provide more information to help locate the proper partition, especially if the partitions are labeled. The device/drive is designated by sdX, with X being the device designation. sda is the first device, sdb is the second, etc. For most users the MBR will be installed to sda, the first drive on their system. The partition is designated by the Y. The first partition is 1, the second is 2. Note the devices and partitions are counted differently. Mount the partition containing the Ubuntu installation.
sudo mount /dev/sdXY /mnt
sudo mount /dev/sda1 /mnt
Note: If the user has a separate /boot partition, this must be mounted to /mnt/boot Note: If the user has a separate /home partition, this must be mounted to /mnt/home. Encrypted home partitions should work.
Run the grub-install command as described below. This will reinstall the GRUB 2 files on the mounted partition to the proper location and to the MBR of the designated device.
sudo grub-install --boot-directory=/mnt/boot /dev/sdX
sudo grub-install --boot-directory=/mnt/boot/ /dev/sda
Refresh the GRUB 2 menu with