Now it has happened twice & have been pulling my hairs now... I have installed xubuntu on my external hardisk & have been using it for about 3 months. It has three partitions, one of 500 mb mounted at /boot, 2nd one of 48gb mounted at / & the rest (out of 160gb) is ntfs partition....used as normal external storage. The last storage supposedly acts as a buffer b/w Linux distributions & Win platform, buffer in the sense that it provides a universal channel for data transfers.

I have constantly used this external hardisk for data transfers b/w win7 laptop & xubuntu (on this external hd) without any hassle. However, on of my desktops where I have ubuntu I (for the first time) attached this external drive which let me do data transfers where all three partitions properly mounted....but then nasty thing occurred the same that occurred before.

I (as usual) tried booting via this external hd (one having xubuntu, one having being formerly used under Ubuntu) I got error

Now I am totally devastated because similar thing happened ~6months before when I had fedora 17 in my external hd (instead of xubuntu) & after it was used under ubuntu the same happened...i didn't reported it because I already had planned towards debian instead of rpm!

The mystery is that as long as I don't attach this external hd under ubuntu the data never** corrupts whereas under win xp/7 I can use it as a normal usb storage of coarse linux partitions aren’t available under win platforms...

**From corrupts I mean hd fails to boot with the error mentioned however cant say whether data within remains untouched? It seems that my grub & or MBR is corrupted. Please sir guide me to solve this issue also why I cant attach & use linux external hds under linux platform

Disk /dev/sdc: 160.0 GB, 160041884672 bytes
255 heads, 63 sectors/track, 19457 cylinders, total 312581806 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0004e7d0

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1   *        2048      976895      487424   83  Linux
/dev/sdc2          978942    96874495    47947777    5  Extended
/dev/sdc3        96874496   312575999   107850752    7  HPFS/NTFS/exFAT
/dev/sdc5          978944    94726143    46873600   83  Linux
/dev/sdc6        94728192    96874495     1073152   82  Linux swap / Solaris

I can recall for sure that have seen a thread here when a similar problem occurred & in response someone gave solution of how to mount (now invisible) partitions & recover important data in them. I have misplaced that URL so if any can guide me thither because my important documents resides in / partition

What I already have done: Without success I have tried this & related solutions

What I plan to do: I believe that filesystem has corrupted & would you recommend solution like this provided I cant recall whether my /boot (500mb) partition was ext4 or ext2 though I am sure that my / (48gb) partition was ext4

UPDATE 1

Attached my external hd under Ubuntu ran followinf command as root

grub-install /dev/sdc

where /dev/sdc was my external hd containing corrupted xubuntu....it reported all done! I re-ran fdisk -l but to my disappointment it reported

Disk /dev/sdc: 160.0 GB, 160041884672 bytes
255 heads, 63 sectors/track, 19457 cylinders, total 312581806 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x1b6b9167

Disk /dev/sdc doesn't contain a valid partition table

...& now I can't even access its ntfs partition (former /dev/sdc3) please help?

UPDATE 2

TestDisk (by cgsecurity) failed at founding any partition table :(

TestDisk 6.13, Data Recovery Utility, November 2011
Christophe GRENIER <[email protected]>
http://www.cgsecurity.org

Disk /dev/sdc - 160 GB / 149 GiB - CHS 19457 255 63
     Partition               Start        End    Size in sectors