Chosen Solution
Put a new reformatted SSD in, which I installed High Sierra onto from another MacBook. Initially it worked, but after I restarted it I am getting the Folder With “?” Mark Into Apple Logo Into Circle With Line & Repeat. What is going on?! Command R button results in just a white screen. Doing option and choosing the recovery drive results in the same problem as the first paragraph. This is a MacBook Pro 13-Inch “Core i7” 2.9 Mid-2012. Thank you!
Did you change the HD cable? You can’t ever trust the factory ones on these with SSDs - the rough chassis wears them out and the SATA II/III lottery makes it so you don’t know if it’ll work. It’s better to replace it with a known compatible cable that’s SATA III ready. Get a new cable for the machine and that always cures these issues. Refer to this guide for a replacement and install instructions. Patch the cable using my instructions on this post before installation.
