hard disk failure
the below links contain information that you need when you encounter hard disk failure, certain type of hard disk failure requires it to be sent to the laboratory to recover your data and in some cases, you can actually do-it-yourself.
http://www.adrc.com/diy_rescue/win/hard_disk_clicking.html
http://harddriveclicking.net/category/click-of-death
ddrescue is a good tool to recover files from bad hard disks with logical errors if you know how to utilise it. anything that is related to mechanical fault on the hard disk, it’s best to send it to the professional.
*hint*Â Please Note:Â if you data is critical to your life and/or business it is always best to seek out professional data recovery services rather than attempt this yourself. Also if your hard drive is clicking, making other strange noise, showing wrong capacity, or not appearing in BIOS you should immediately power it down and seek professional advise.
http://www.forensicswiki.org/wiki/Ddrescue