16km Atmosphere question

[siber]

Hi all. Sorry to disturb with another technophobe question...

I've just put GWX2 onto my system and have enabled 16km atmosphere. However, now, the sky has funny black lines and scratches appearing above the horizon. Reading the other threads on the forum, people have mentioned nVidia graphics cards (which I have) as a source of problems, but I'm unsure whether this relevant to my problem. I'm also a real computer wannabe who fall down on understanding them, so wouldn't know how/where to start diagnosing and fixing any problems...

I'd appreciate any assistance or advice you could provide. Many thanks in advance...