|My apologies, probfixer. Looks like you may have been right all along. :)|
Still, run SpeedFan anyway just to get an idea of how hot the system is getting...you never know. A CPU above 70C is a cause for concern.
Have you tried running the seemingly faulty stick of RAM by itself?
Does your motherboard have a Molex power connector near the PCIe slots? If it does, it should be connected to the PSU when you're running two video cards. Many older Asus SLI boards (such as the one I'm using) have this connector; newer ones don't.
Have you tried running Memtest86 on the various memory combinations you've tried?
And last question of the day: Do you have another PC you can test the RAM (and video card, if necessary) with?
Now fully Se7ened.