Hi Lickitung
First of all, you've almost the same configuration of my PC, it can be said that they are twins
If you have a Gygabyte motherbord sure they are
BTW, I've the same CPU and the same GPU, I overclocked the processor to 3.0 Ghz and I've 4 GB of memory.
For what concerns the stabilty of your system, supposed that you're running it with no overclocking, the crucial factor is the memory modules, I found that a cheap brand brings the PC to some crashes, so I suggest you to test the memory for some ours with an application, for example MEMTEST and in case you've a lot of errors, just buy better modules.
About atmospheric effect, it's resource consuming and have a lot of settings here and there, included the lights, it works better in a scene with props, like walls and object and the easiest way to set it up is in the material room, there click on "create atmosphere", then select "object" and "atmosphere" to trim the values. But for all the options you should refer to the manual. I found to have better results with postwork BTW.
You should run at 4 render processes, 'cause you've a quad core, separate process unchecked is ok, the memory buffer, I changed it but I've seen no effects.
I suggest you to put the "max bucket size" value at a low value if the scene is complicate, first setup firefly render in automatic setting, then change to manual, import from automatic and change the value. You may better upgrade P7 at SR3 if you haven't already done it, I remember something related to hair that was fixed with a SR but I'm not 100% sure of it.
You could build a simple scene and change the value till you find the optimal setting. Render dynamic hair alone and see what happens...
Actually I'm no more running
Poser on Windows but on Mac Os, it's a a little more stable but it's not that it doesn't have problems

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Mac Os on my PC ... Yes it is

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