Regarding power consumption, the PS would not be an issue at idle (2D). I noticed you said both are plugged in right now? SO you have a large PS that has at least (3) 6 pin power connectors? Your 6850 needs 1 and the 7950 needs 2, correct? Unplug the 6850 and use the 6 pin power connector on the 7950 and swap them around to make sure one of your 6 pin power connectors is not the problem. You can even use a volt/ohm meter, just to verify the 12 volt output on the power pins ( there are three pairs of 12v and ground ). Just measure voltage, not amperage, the amperage will vary with load and your meter may not be able to handle the current. Make sure all of them read the same. If everything checks out then you can start assuming it is defective. I would probably still want to try it at a friends in another computer, or call the manufacturer. My first 6950 was bad and I called Sapphire and we went over a bunch of tests and they told me to send it in!