My general specs are AMD 6000 (89W), 4GB memory, ATI4850 Vapor-X + DVD + 60GB SSD
First high quality 500W PSU died (no boot) so replaced with another High quality PSU of a differing brand.
Machine now starts correctly, doesnt over heat (too my knowledge - I can run Orthos + Furmark + Atitool together for 18hours with no issue).
However ... after about 2.5 hours of SIMS3 the machine will consistantly black screen and the Motherboard fan will blow at full whack until you reset power. To my knowledge this is the only application where this will occur.
Any Ideas? - can applications screw a system that bad? Im not sure this a software or hardware issue...
From what you've described, I think there's something wrong with your power supply or at least the power cables connecting that to your components. Also, have you tried using the computer with another wall socket? There could be some grounding/current problems with the one you're using now.