Solaris-RHEL5 Dual boot issue

Machine: x86
OS : Dualboot Solaris and RHEL5 -Solaris 10 in first fdisk partition.
RHEL5 - /boot in partition2
/ in partition3
swap in 1st logical partition (/dev/sda5)
GRUB : Grub of solaris 10.

Both OSes were working fine, today when I booted the system, it is just showing the 'grub >' prompt.

I tried with manually typing
grub>root (hd0,0,a)
grub>kernel /platform/i86pc/multiboot
grub>module /platform/i86pc/boot_archive
grub >boot
but once i type grub> root (hd0,0,a) and pressed 'enter key'

it shows unknown filesystem---type xbf

Now, what should i do to restore the grub of Solaris and to make it work as before...?
I tried installgrub -m /boot/grub/stage1 /boot/grub/stage2 /dev/rdsk/c0d0s0
it is overwriting, but when i rebooted, i see the same old grub> prompt...
please help.

Did you try to use any recovery CD?