Howto use a rescue mode install cd ....with images for some problems
 

Disclaimer, do at own risk

I intend to show short sharp instructions with more pix to illustrate to newbies how to do stuff. I know there are other ways, and I will have a sister howto on live cd. For these pix, I ran various distros in virtualbox to allow easy snapshots to be taken.

Change bios boot order to allow optical drive to boot before hard drive

boot your normal install cd or dvd....and hope its got a rescue mode. It may be called recovery.
http://h1.ripway.com/aus9/rescue/rescue.png

after the rescue system has booted you normally arrive at some menu.
http://h1.ripway.com/aus9/rescue/menu.png

It is highly likely you have no mouse at this stage so use the arrow keys, the ESCape key, and my favourite TAB key...along with ENTER of course.

my post 2

Lets try automatic re-install bootloader which is already highlighted.
Press the TAB key to go to OK button
http://h1.ripway.com/aus9/rescue/autobootok.png

press enter.....distro tries to find booting files to suit structure.
http://h1.ripway.com/aus9/rescue/auto-mount.png

read your options and type ok if you want to proceed
http://h1.ripway.com/aus9/rescue/auto-ok.png

and hopefully you get this
http://h1.ripway.com/aus9/rescue/grubdone.png

press enter to leave that sub-menu area

If that is all....reboot and remove disc to check you now have grub in