A good friend suffered a major problem with his hard disk which rendered the machine unusable (wouldn't boot). I used some analytical software which I had which diagnosed problems with the hard disk.
Like so many he had vast numbers of photographs on the disk and no backup.
I took a chance on some software called Spinrite. It took 22 hours of continuous (automatic) reading and rereading of the disk to to repair the damage to the point where the machine would boot and all the data was recovered. We copied the data and threw the disk away.
First purchase of the software is around US$90 but it did work for me and my pal thought it was a cheap price to pay to recover his photographs!
I have no connection at all with the company who write the software.