Call me crazy but rather than blindly trying various distros in the hope that the problem would magically disapper I'd have done something like:

1) Google "grub error 18"

2) Click link for the top result - http://wiki.linuxquestions.org/wiki/GRUB

3) Read the table of contents

4) Click link for the section devoted to the cause and fix for this exact error

5) Follow the rather simple directions