Hello! This may sound obvious, but did you check in the lens flare options to make sure thatit was still turned on for the sun? If so, then you may have found a new bug. It's not happening at least in my PC version of 4.05. Now, that's only if it's the lens flare sun you're talking about, and not the "normal" sun you see when you have "Size of the sun" turned up under the Sun tab in the atmosphere editor. if that's the case, it doesn't work for me either when swiching to volumetric atmosphere. Now, you'll find that if you turn up the "Haze" slightly, you should see your sun appear, and you can change the haze color to a better sun color other than blue by double clicking on the little colored bar there. As for everything going all black, yeah. It takes some getting used to, but you absolutely have to have some degree of fog in the scene, and/or haze. The nature of volumetrics, I guess, since it's supposed to be simulating an atmosphere filled with particles of all sorts.