Computer froze, after that flashing folder with questionmark.

Hello everybody,

One month or so ago, I replaced the HDD of my MacBook Pro 13" early 2011 with a Samsung 850 EVO SSD. All worked fine until today. I was running a few apps when the computer froze and did not respond anymore. I held the power button and tried to reboot. Instead of the Apple logo I saw a flashing folder with a questionmark.

The weird thing is that when I put the original HDD back in, everything works fine. After swapping between the drives a few times nothinh changed. The cable that connects the drive to the board has once been replaced before and this (I think) can't be the problem.

Do you have any ideas?

Thanks in advance!