Chosen Solution
after I had the famous folder with the question mark and I could no longer see my hard drive in the internet recovery menu, I thought that this might be a defective HD. However, it was recognized with USB adapter on my other Mac and I could also boot on the “defective” Macbook by USB adapter. So only the hard drive cable remained as a possible problem, since this seems to be the case very often. So I ordered a new one from the ifixit store and just installed it, but the problem was not fixed. The hard disk is also not recognized with the new cable, even after I have formatted it with the USB adapter on the other Mac. I really hope that someone knows what this could be or how it could be fixed. :) Tobi
When that cable gets damaged by being either hit on the upper ledge or from the hard drive sitting on it and vibrating against the bottom rough surface, it can also damage the data of the hard drive. If you have another bootable USB disk, hook up the original externally and the other USB drive (now the boot source), and run Disk Utilities on it.
