It seems that your MBR has been corrupted.
Please run the same installation CD in the rescue mode and mount the HDD somewhere (say /mnt itself). Or any other CD (even Linux would do but with a slightly different trick).
Now change the root using
sudo chroot and fire the
grub-install command with the same GRUB configuration, you earlier had, which you should be able to get inside the /boot directyory.
Now comming to the use of a Linux CD in the absance of your original solaris CD; what you need to make sure here is that the same GRUB configuration is installed to reboot to get
that GRUB menu. I think, here you don't need to do the chroot (else you'd get a lot of floating point error or other host of errors even seg-11
); instead copy
that grub.conf file from your solaris partition's /boot (ofcourse you need to mount the HDD somewhere to get the copy of grub.conf). Put the configuration file under either /etc/grub/grub.cong or /boot/grub/grub.conf and fire the command
grub-install . Once you see this command returning to give you the root prompt after the run; please reboot your system by removing this Linux CD.
You should be get going, untill you have a really hard luck today.
Beat of the Luck.
Cheers!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!