Agree with Bruno, we could help better with screen dumps showing the render and light settings, etc.

As suggested, you could drop back to a simple default scene and keep your default (Final) render settings, then render small samples or small area selections on your main PC and troubleshoot from there.

Deleting the sun is okay, but your point lights do need that "Apply settings to all lights..." enabled, from what it sounds like. There is that flat black sky, in the SKys > Effects > others that's good for black scenes, space images, etc..

If you're using volumetric spheres, is volumetric lighting type required? Experiment with a small image.