Failed to boot Grub Error Fedora 17

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http://unix.stackexchange.com – I had two hds one 320gb all ntfs, it is internal where win7 is installed in ~20gb partition next is the external drive 160gb where I have installed Fedora. Now when I had installed fedora I completely dis-attached my internal hd so there is no relationship b/w internal hd (having win7) & external... I had installed Fedora17 32bit on my external drive 160GB & I was loving it for about 2 weeks...However something bad happened & now whenever I boot via external drive 'Grub Error, unknown filesystem' emerges & I can't proceed. I had been using following partitioing layout: (all as (HowTos)