Can't find old HDD

[Monkeyman]

Didn't seem to work.  I did what you said but when I entered the last command in terminal, this is what I got:

monkeyman@monkeyman:~$ sudo mkdir /media/external
[sudo] password for monkeyman:
monkeyman@monkeyman:~$ gksudo leafpad /etc/fstab
'monkeyman@monkeyman:~$ sudo mount -a
[mntent]: warning: no final newline at the end of /etc/fstab
NTFS signature is missing.
Failed to mount '/dev/sdf': Invalid argument
The device '/dev/sdf' doesn't seem to have a valid NTFS.
Maybe the wrong device is used? Or the whole disk instead of a
partition (e.g. /dev/sda, not /dev/sda1)? Or the other way around?