I had the same issue with my Macbook Pro mid-2012 13-inch. The symptoms would gradually progress like this: (1) after taking laptop out of my, it would be frozen (black screen, breathing light stuck to 'on') (2) when picking up the laptop while open, screen would display those horizontal stripes / blocks (3) shortly after that, it would progress to the three-beeps situation and not being able to find the RAM (4) there were side effects, like a confused Wifi and MS Outlook crashing its identity, but those were symptoms not causes After taking it to the repair folks, it would often work without problems again for a long time, even though they had no clue what the cause was. Strangely, taking the RAM sticks out and plugging them back in was not always effective. Or not for long. But sometimes it was. I was so happy to read Santiagodelatorre's analysis. *That* finally made sense to me. And his solution seems to work for me too. At the end of the RAM clips, there are little round protrusions that fit in a round...