Here is introductory information about how to prevent hard drive crashes, and how to recover data from a damaged hard drive (for free in some cases). Please feel welcome to post whatever helpful information you have about these subjects in this thread.


Computer users should regularly run a diagnostic or system information program to check the SMART (Self-Monitoring, Analysis, and Reporting Technology) values of their hard drives to find out if their hard drive is in danger of crashing. The web site of your hard drive manufacturer should offer a free downloadable diagnostic program for your hard drive.
More information about SMART:
http://en.wikipedia.org/wiki/S.M.A.R.T.

S.M.A.R.T. attribute list (ATA):
http://www.hdsentinel.com/help/en/56_attrib.html

Be wary of running a long diagnostic test on a damaged hard drive because that might cause a damaged hard drive to die permanently. Just run the short test.

Hard drive crash preventive measures:
Be sure that your computer and hard drive does not overheat.
Turn off your computer hard drive when not in use, for example by using your operating system's power saving settings to automatically put your computer into standby or hibernate mode or turn off hard drives after a certain amount of time. (In Windows XP this is: right click on desktop, properties, screensaver, power...)
Be sure that your computer is on a level table. (By using a "spirit level", one of those tools which has liquid and a bubble in it. You should be able to get one cheaply at a dollar store if you don't already have one in your toolkit.)
Use an uninterruptible power supply to prevent your computer from suddenly turning off during a brief power outage.
Back up your important files (obviously).
Stop using your computer other than to back up your files immediately if you start hearing clicking noises ("the click of death") from inside your computer or if you have any other reason to suspect that your hard drive is damaged.

Sometimes when a hard drive seems to be crashed you can still get it up and running temporarily for long enough to back up your files:

By reconnecting the hard drive and accessing files on the hard drive as the second hard drive inside a computer rather than as the hard drive which you boot to.
By trying a different way of connecting the hard drive to the computer (USB, firewire, internal).
By accessing the files on the hard drive from a different operating system.
By turning the hard drive upside down or sideways before running it.
By cooling the hard drive before trying to run it. (e.g. by using an electric coffee cup cooler or refrigating but not freezing it. You have to not cool it to the point where condensation of water might occur inside your hard drive.)
By running the hard drive in PIO mode rather than the usual and faster DMA mode(In Windows these settings can be changed in Device Manager). (This is my source for the advice about PIO mode: http://www.myharddrivedied.com/presenta ... paper.html )

According to Scott Moulton, data can be recovered from 85% of crashed hard drives without having to open up the hard drive and replace parts, doing it just by using special disk imaging software (or the above techniques). To do disk image backup you should have a completely empty hard drive to back up onto and this hard drive should be the same size as, or larger than, the hard drive that you are trying to back up. You need to use a specialized type of disk imaging program, one which does a few tricks such as not hanging when it tries to back up a bad sector and preferably can disk image in the reverse-from-normal direction. SMART monitoring should be turned off in your computer's BIOS/setup program before you do the disk image back up. Remember that you may get only one opportunity to do the backup before your damaged hard drive dies completely, so you should preferably have already practiced doing disk image backup and know what you're doing.

There are a couple of free Linux command line programs which can disk image copy a damaged hard drive: DD_rescue with DD_rhelp, and DDrescue. (DD_rescue and DDrescue are two similar but different programs). However they lack a user friendly GUI and documentation for them is rather sparse. There are a few free downloadable bootable CDs which will run these programs.

More info about hard drive data recovery:

41-page course outline about hard drive data recovery:
http://www.myharddrivedied.com/DataReco ... utline.pdf

My hard drive died/Scott Moulton course, distant learning:
http://www.myharddrivedied.com/presenta ... rning.html

Youtube videos about hard drive data recovery by Scott Moulton:
http://www.youtube.com/profile?user=Sup ... =playlists
http://www.youtube.com/watch?v=Kx-D1nJcv0k
http://www.youtube.com/watch?v=vCapEFNZAJ0
http://www.youtube.com/watch?v=zUyxIG0xsBg

Data Recovery Blog
http://www.hddoctor.net/

Another crash prevention tip:
Dropping an external hard drive, or a laptop computer, once may be all it takes to make it stop working, something that you need to consider before you buy one. The reality is that everyone is clumsy enough to drop something sooner or later if he/she carries it around enough. I would suggest being ultra-careful when carrying a hard drive or laptop, gripping it firmly with both hands, and carrying it in some kind of pouch with a strap around your neck so that it wouldn't fall even if you let go of it with your hands. Also store it safely in a locked room, drawer, or filing cabinet when not in use.

I also forgot to mention:
Some Computer BIOSes/Setup programs will also allow changing between DMA and PIO mode.

Mr Mikefree you have just been crowned Mr SA of the week, congratulations!, SA? Ask BlackST...

Here is another .pdf (97 pages) by Scott Moulton, titled DIY(Do It Yourself) Data Recovery Diagnostics, about how to diagnose a hard drive failure, about which software to use to do disk image backing up from a damaged hard drive, and more. It's full of illustations:

http://www.myharddrivedied.com/phreaknic13/diyhdd.pdf

(I found the link to this pdf file on the Disk Labs data recovery forum:
http://www.data-recovery-forum.disklabs ... .php?p=660

And on myharddrivedied.com :
http://www.myharddrivedied.com/phreaknic.html )