Blender freezes when rendering,building the last samples Out of sudden the Blender freezes when rendering on Cycles.Always at the same moment.When the image is almost done,that is to say Path tracing title is done 135/135 and it's building up samples,at the last point it stops working.I made all the updates to mac OS and using the last 2.78a version,even though it started on 2.77

I thought it was the project's problem so I opened different project and it does the same thing.I'm completely stuck and unable to render anything.Sometimes it renders one frame but the following gets stuck again.
Is anyone else experiencing this? I have no idea what it could be?
Thanks so much for any help.
For laptop users:

On any render, my computer (the whole screen) would freeze about 5 seconds, and after some seconds it would freeze again.

To fix, I had to go to File -> User Preferences -> System and on the bottom-left side I picked CUDA for the "Cycles Compute Device", and this fixed the problem.





It seems very noob-ish because it actually is! And it worked for me since I am a beginner, I hope this helps another beginner searching this on Google.