which distro you are using?
If its Fedora/RedHat try the following,
Boot using first CD enter
in the starting screen answer the question (defaults ok) it will take you to a rescue prompt, there enter the following
Code:
# chroot /mnt/sysimage
# grub-install /dev/hda1
/dev/hda1 is just for an example replace it with your real linux boot partition.