The hard drive crashed on my daughter's mid 2009 Macbook Pro. I removed it and tested on another machine and it was dead. I decided to replace with an ssd, which I had done on an imac and an air without trouble (with ifixit's help). The pro's drive was much easier to access. But the computer did not recognize the ssd. I read about all of the problems that the mid 2009's have with both ssd's and hard drives and so tried a hybrid, then 2 hard drives - same problem. I finally decided to spend the $50 and try replacing the hard drive cable. It worked.
This was a relatively easy and quick repair - just one step beyond the hard drive.
ifixit is playing an important role in giving people the support and tools they need to do their own computer hardware repairs. My situation demonstrated one of the challenges of do-it-yourself repairs. If I was a repair shop and had cables in-stock, I would have tried a new cable when the first drive did not work (which was an ssd - I ended up with a hard drive because that was what I had when I tried the cable and I was not going to take the additional step of exchanging again to try the ssd). But I did not spend the $50 until I had tried the other options (options that seemed reasonable based on others' reported experiences). It took several attempts and a lot of research time - but it worked and I continue to learn from these repair experiences.