Originally Posted by Tumbleweed36

Try it with only one card and see if it reboots. Also, are you certain that all the dust bunnies have been cleaned out of those fans including the CPU fan and heatsink, all case fans, any chipset fans, and last but not least, the video card fans.

You may be a tad light on power supply juice with a 580 watt Tagan (not a bad power supply, although the available juice might be a little light for this rig IMHO) and that can also cause what you are seeing. If this were my rig, I would go consider trying something like a 700 watt power supply. Do you know anyone who has a larger one you could swap in for a few minutes to try it?