that is alot of power hungry equipment. I would kinda suggest a power supply shortage but then again I dont want you to go buy an expensive psu and it not be the problem. I suggest keeping an eye on your voltage rails especially the 12V rail and see if you are having any dips etc, which would cause system instability at full loads. You can add up your power consumption by just adding up the power requirements of each component....here is a great review you should read.
I would also suggest the memory idea the last guy suggested along with checking the bios to make sure you arent running your memory timings too aggressive for the generic ram.
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