'Unable to mount Filesystem' Error

Solution 1:

For those who are still looking for an answer:

If your HDD is "bricked" and cannot be mounted properly, there are some things to do:

• make an image, if you have the space.
  Operating on an image file won't damage the data on your harddisk, in case you make mistakes and destroy your data.

• if you still can mount your partitions, mount it read-only.
  Alter the mount command like so: mount -o ro /dev/sdb1 /mnt/targetfolder

• If you cannot mount your harddisk's partitions, try extundelete or testdisk:
  sudo apt-get install testdisk extundelete. Then, run cd <recovery-dir>; sudo extundelete /dev/sdb1 or sudo testdisk /dev/sdb1 and follow the instructions to recover your data.

I successfully recovered data from a overridden raid 1 drive, so I can really recommend these tools.