At the grub prompt type in ls
you should get an output like (hd0) (hd0,msdos1) or (hd1) (hd1,msdos1)
now we need to find the boot directory
run ls [partiton name] so if ls does indeed show (hd0,msdos1) that would be ls (hd0,msdos1)
an example output should be - lost+found var/ dev/ run/ etc/...