Well, i'm not sure what's going on, but I do know how to enter a rescue mode.
When the grub boot menu comes up and starts counting down, hit a key and it will stop. Then, select the kernel you are trying to boot from(default one at the top is probably it) and hit 'e'. After this, look for a line that starts with kernel and hit tab(not sure about this one, might still be 'e', it'll say at the bottom of the screen) and add 'single' (without the quotes) to the end of the line. Then press 'b' to boot(or whatever the instructions say).
EDIT: Though, i think it will still follow the rules about the shell, so if that is the problem i think it still won't work.