Could you tell us the exact error message you get at boot (error 15 or error 22 ...) ?
You can restore the boot loader from the liveCD like this :
Once started, GRUB will show the command-line interface (see Command-line interface). First, set the GRUB's root device4 to the partition containing the boot directory, like this:
grub> root (hd0,0)
If you are not sure which partition actually holds this directory, use the command find (see find), like this:
grub> find /boot/grub/stage1
This will search for the file name /boot/grub/stage1 and show the devices which contain the file.
Once you've set the root device correctly, run the command setup (see setup):
grub> setup (hd0)
This is a quote from the grub manual