My 3TB Seagate external HD is seen but no longer recognised

[Vicente Jerez Fidalgo]

I am running Ubuntu 11.10. My trhree 3TB external Seagate Go Flex HDs used to work very well. They were formatted with ext4 fs (if I remember correctly). The problem is that I can no longer mount them and access the contents. The HDs are seen by the Disk Utility but it is not possible to mount them anymore. I did nothing out of the ordinary to the them. The data within these disks are all my phd results; therefore, very precious to me. When I do fdisk -l, the message displayed says something about size being 4096 (not 512). I have tried everything: google, loading live newer versions of Ubuntu, etc. Nothing seems to work. Any help would be very much appreciated. Thanks.

Note: when i run apt-cache policy pkgname, I get "N: Unable to locate package pkgname"

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: gnome-disk-utility 3.0.2-1ubuntu2
ProcVersionSignature: Ubuntu 3.0.0-17.30-generic 3.0.22
Uname: Linux 3.0.0-17-generic x86_64
ApportVersion: 1.23-0ubuntu4
Architecture: amd64
Date: Sat Jun 9 01:56:23 2012
ExecutablePath: /usr/bin/palimpsest
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release amd64 (20101007)
ProcEnviron:
 PATH=(custom, user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-disk-utility
UpgradeStatus: Upgraded to oneiric on 2012-03-11 (89 days ago)

[dino99 (9d9)]

This version is no more supported and is not a 'security' problem; so does not expect a backport