In the last few years I’ve had two hard drives fail. As a last resort each time I put the drive in a freezer for about half a day and then managed to recover most of the data.
WARNING: If the data on the failed hard drive is very valuable to you then get professional data recovery advice. I tried numerous software recovery tools and none of them worked. I was not prepared to pay out for physical hard disk recovery, so I decided to try freezing.
On the most recent HDD failure I noticed that it made a clicking noise. The PC displayed a “no operating system found” message and the drive was inaccessible on other PCs. First I tried putting the drive in a freezer for a couple of hours but this did not work. I then left it in the freezer for about 14 hours and then it worked. Note that if this works there will probably be a limited time in which you will be able to use the drive, so copy the most important data first. The first time I had long enough to copy the entire drive but the second time I only managed the get about half of the data. Don’t forget to put the drive in a plastic bag or two before putting it in the freezer.
It seems that science behind this is that the components in the drive shrink slightly when cold. This tightens up mechanical parts that might have become loose and could improve electrical contact issues.
Not wanting to push my luck too far, I am now using RAID mirroring with two hard drives!