I think "file not found" refers to the grub.cfg file. Please post the output of "set" at the grub rescue prompt. Does the "prefix" look correct? You can change the prefix at the grub prompt with, for example
Use the ls command to find the correct path. (Search works only if the search module is loaded). After the prefix is set correctly, then:
will bring up the grub menu.
If that works, then the final step is to save the environment permanently. I don't know how to do that yet. (I'm having the same issue).