No, that's not the problem, because the objects redered at first, but now the whole scene (starting with the sky that is supposed to be blue) just stays black after rendering the buckets. It's like nothing happes, but something must be happenig because the program uses cpu, but nothing is displayed. The GI dots are displayed correctly though.
This is all very strange.
I could try to render on my other pc, but that is rendering a HQ scene right now, and not even close to finishing for the next week or so.