If possible boot a live cd, any live distro will do.
You need to go to: /boot/grub/menu.lst
In the folder /boot/grub
there should also be a menu.lst_old (something like that). Hopefully this is the file with your old settings. You need to right click open with kwrite or kate.
Do the same with the current menu.lst and compare the two. Change the current file accordingly.
Another thought. Did you try a failsafe boot. It should work shouldn’t it? So you may be able to boot from that and edit from your system, rather than from a live cd.