What is it? It sounds... out of the ordinary for someone at home - more technical shop or something.
It's linux, so it's not really technical shop but it's not an ordinary user thing either. Pretty much you just plug in the device, run "fdisk -l" and look to see if the device is in that list. If it's not, chances are it's dead. If it is, run "mount /dev/sdx# /mnt", where sdx# corresponds to the device partition (example being sda5.) If it mounts, the device is fine. If otherwise, something's wrong with the device.