I have given the thread a better title........remember the sign in the store: "We have just two speeds here---if you don't like this one, you surely will not like the other."
First, RHEL 3 is pretty old (obsolete).
Second, how did it get this way? (It **appears** that something was changed such that GRUB cannot find it's config file.
It sounds like you have the GRUB command prompt-----do you see this?:
If so, you will be able to manually enter the commands to boot your OS--see the GRUB manual for details.
Your other option is to boot from a live CD and re-install GRUB + a valid config file.
Your BEST option is it install a more modern distro.