The moral of the story is try each partition until it works =p.
error. No such partition.
Grub rescue> ls /boot.
error. No such partition.
Grub rescue> ls.
(hd0) (hd0,msdos3) (hd0,msdos2) (hd0,msdos1).
This is a comment. The following is choosing the non linux partition by mistake... error unknown filesystem should alert you to the mischoice. Keep choosing until you get the right one!
Grub rescue> set prefix=(hd0,msdos1)/boot/grub.
Grub rescue> set root=(hd0,msdos1).
Grub rescue> set.
Prefix=(hd0,msdos1)/boot/grub.
Root=hd0,msdos1.
Grub rescue> ls /boot.
error. Unknown filesystem.
Here I choose the correct partition - an ubuntu one. Note that the ls /boot doesn't give an error!
Grub rescue> set prefix=(hd0,msdos3)/boot/grub.
Grub rescue> set root=(hd0,msdos3).
Grub rescue> set.
Prefix=(hd0,msdos3)/boot/grub.
Root=hd0,msdos3.
Grub rescue> ls /boot.
Blah blah blah loads of stuff, I'm not going to type it all out... its similar to the junk about generic and abi from the blog thing.
Grub rescue> insmod /boot/grub/linux.mod.
Grub rescue> linux /vmlinuz root=/dev/sda3 defaults.
Grub rescue> initrd /initrd.img.
Grub rescue> boot.
________________.
#Booted! Its TERMINAL time! Open your linux terminal and plonk this in. Credit to http://techgage.com/news/repairing_a_broken_grub_2_boot-loader_on_ubuntu/.
Sudo update-grub.
Sudo grub-install /dev/sda.
