Well, the cheapest & most reliable way is to just bin that disk & recover from your backup to a new one.

It wasn't the OS crash that caused the damage; rather, the disc suffered a major hardware failure and this caused the OS to crash. The cause of the failure could be overheating or another cause of failure of one of the mechanical parts: motor, bearings, head servo, dust intrusion, etc. It is probably worthwhile to let one of the other data recovery firms have a look at it: if the problem is simpler than your first analysis suggests, then they ought to give you a much lower cost for recovery. Otherwise, follow @Tetsujin's advice.

What are your beliefs based on?

@Tetsujin Unfortunately this disk was the backup. And I bought it 3 moths ago. Who would know it would fail so soon? I had all of my personal data stored on this disk. Also as a junior developer (multiple languages...) I kept all the projects on this drive. In few words, i have lost every important piece of digital data with that disk.

"Any data stored in less than three distinct locations ought to be considered temporary". If it's the only location... how is it 'your backup' ?

@Tetsujin I meant, that my computer is failing from some time, and in order to keep the data save, I have been working on an external drive, omitting my computer internal drive... Yeah i know i was asking for troubles...

@gronostaj On intuition... It was highly unlikely that simple OS freeze could cause all of this... But AFH made his point also...

@Tetsujin definitely data backups. But for my defense i have to say that i had a very long and very successful relation with my older HDD (years ago). And i just took it for granted that new HDD from a well know firm (Western Digitalis) will do the work. BTW to clarify things, my OS resides on the internal HDD, all of my data had been stored on the external.

@AFH thank you for the explanation.

Actually, hard disks are slightly more likely to fail just after buying than a bit later (see bathtub curve and this Backblaze blog post).

@Tetsujin A MIRACLE HAS HAPPENED !!! I plugged in the drive. To my surprise it mounted, I opened the file system and i saw that all of my files are intact. I copied single THE MOST IMPORTANT project from the external HDD, and then it crashed again... I am still able to mount this drive but I am unable to view file system. I don't want to push my luck, therefore the disk goes back to the shelf.

@gronostaj I know for sure, that disk surface is intact, that disk head is also OK (or at least was OK). I believe that some other piece of hardware suffered damage. Most probably USB - SATA bridge ?

Possible duplicate of How can I efficiently recover a permanently deleted folder at once?

@karel how is this a duplicate? This question is about recovering data from a (ALMOST) DEAD HDD not recovering deleted file from a working HDD... Sorry but are you trying to get reputation at my expense?

The author of the accepted answer is the developer of a free software called RecuperaBit designed especially for recovering data from damaged NTFS hard drives. This may be your best chance of recovering the data from your hard drive. Recommending esoteric software is if anything potentially damaging to my reputation if not for the fact that this software is possibly the best software to do the job Please also read Andrea Lazzarotto posts about RecuperaBit on Ask Ubuntu Q&A, starting with this one: askubuntu.com/questions/775579/…

@karel Thank you for this information, I will look into this tool, and if it will do the trick, i will buy you a beer! (probably I will have to ship it across the world in the first place...) Also I am sorry for my accusation... Very sorry... I did not get your intentions right in the first place, and I did not understand what you done. Now its clear and I am ashamed.

I have read in several places that a failing drive can be resuscitated temporarily by putting in a freezer for several hours (after wrapping it in several layers of moisture-proof polythene). The fact that your drive came back to life briefly suggests that this may be worth trying. Before you remove it from the freezer and connect it, be prepared to copy the drive: you can use something like sudo dd if=/dev/sdX of=TargetFileOrDevice bs=64M conv=sync. The last clause is important, to prevent disc errors offsetting the data on the copy, but it may make the output file slightly too large.

Once you have the copy, you can restore it to a fresh drive and then whatever files are recoverable should be on it. Make sure you write-protect the copy, as you may never get another one.

@AFH instead of wrapping in fancy things just use a zipiock freezer bag, and make sure it is sealed tight.

Your hdd is dying, and the OS freeze is a symptom, not the cause. You have 1 maybe 2 chances to get your data back, if that. You need to have new larger drive at the ready to copy ALL your data onto. You can do the freezer trick, and then dd. There is also spinrite by grc research. grc.com

problem with this disk evolved into an inaccessible HDD. It is being mounted upon plugging in but I am unable to access the file system. Disk backs to life periodically (once every 10 or so hours) just to let me copy a single file. After that's done it fails again.