Fixing a corrupt GRUB MBR on RHEL 4

Use grub-install to fix:

# chroot /mnt/sysimage
# /sbin/grub-install /dev/hda
# quit

or

# /sbin/grub-install --directory="mountpoint" /dev/hda

where "mountpoint" is boot partition

If above steps fails try the following :
Launch a grub shell:

# /sbin/grub

grub>root (hd0,0)
grub>setup (hd0)
grub>quit

Create grub password :

# grub-md5-crypt
password : password
retype : password

Copy encryption password to /boot/grub/grub.conf under hiddenmenu

# vi /boot/grub/grub.conf

----------
hiddenmenu
password --md5 ialknda$SDLKANDADikaldnald9addasdad
----------