Power sounds as plausible as anything else at this point. I'm no engineer so I don't know how much the increment in CPU usage is from Poser to say Bryce. If the PS was borderline anyway (defective/undersized) it could happen. I'm wondering though if you have a CPU crash or memory error why don't get a Windows error message (or why the system doesn't just freeze)? It seems as if the thing is cutting off the video or sending out an illegal video signal before the throwing an OS error so you get the video signal error. It's almost as if it is video related. I don't know enough about hardware to know if that's valid. The only other non-expert suggestion I can think of is get ahold of a benchmarking or diagnostics utility that will put a load on the CPU and memory, preferably maxing them out. If it crashes the same way then you should hopefully be able to narrow it down to one or the other. It's fun to speculate on possible causes but I know it's no fun for you. I hope you get it figured out soon.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken