SSD in a MacBook Pro (mid 2012, 13"), Finder symbol with question mark I am having trouble upgrading my MacBook Pro (mid 2012, 13") with a SSD.

3 weeks ago, I installed the Samsung Evo 840 (500 GB) into my MacBook Pro. It worked fine for 3 weeks, then two days ago, my MacBook freezes. I restart it, and a Finder symbol with a question mark appears. I open Disk Utility in several ways (connected my old HDD through USB, or used cmd + R), it shows the SSD but I can neither repair nor verify it. When I start the MacBook Pro, it tells me that it cannot read the internal SSD (or something similar). 

Then, I installed the MX100 Crucial SSD (500 GB). It works fine from USB, but once I install it inside my MacBook Pro, I again get the Finder symbol with a question mark. Same for the Samsung: it works via USB, but once its inside, I cannot boot from it. 

I installed the HDD back into the MacBook Pro, and it works fine.

I didn't find anything similar to my problem on the web, so I'm asking here. What could be the problem?
I'm guessing the problem is the cable that connects your hard drive to the logic board.  You can order a new one from eBay, Amazon, or other Apple suppliers, or set up a Genius Bar appointment to have them diagnose and see if it is the issue.
A family member and I both had similar issues with our MacBooks.