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?