Try a live cdrom like Knoppix or whatnot. There are a few. Some are quite small (a few megs), but knoppix is so slick!
mount the linux root partition to something like /mnt/harddrive
Then mount /boot if you have that seperate.
cd /mnt/harddrive
edit /mnt/harddrive/etc/lilo.conf
make sure that is nice,
chroot /mnt/harddrive
lilo
and then exit out of the chroot enviroment, unmount everything and then see if it reboots properly.