If your MBR is wiped out the easiest solution is to re-install grub. If you have a “rescue” disk this may be simple, but in my experience it almost never is. The solution is to install boot with knoppix, mount your root partition and mount the /dev/ and /proc/ directories inside the chroot. Depending on your partition structure, if /boot/ is a separate partition you’ll need to mount that inside as well.
Warning: Don’t enter any of these commands unless you know what you are doing
mv /mnt/hda1/dev /mnt/hda1/dev.backup
mount -o bind /dev /mnt/hda1/dev
mount -o bind /proc /mnt/hda1/proc
Bob is, quite literally, your uncle.