I wasted some time on Friday trying to get a machine with grub 2 installed to boot.
The machine booted into Grub’s rescue mode. Grub 2′s rescue mode is nice, but not exactly intuitive (no ‘help’ or ‘?’ command), and documentation for it is apparently not easily found via Google.
This is what was eluding me for a while:
In rescue mode, only the insmod, ls, set, and unset commands are normally available. If you end up in rescue mode and do not know what to do, then see "GRUB only offers a rescue shell."
That’s from the Grub manual at gnu.org.
The steps involved in recovery are documented in the same manual. Basically you need to set the prefix and root variables, and then insmod the ‘normal’ module and run it.