Using strictly DVI. I just plugged my xbox 360 (VGA) using an adapter to DVI and it works fine. Monitor is fairly new... HP 2009. Purchased it in 2010. Maybe a little old, lol.
@ss202sl wouldn't it still show a display even if its low?
In this case ur monitor and cables are out of the equation.
The reason that i've asked to test out with the single card is due to the fact that ur PSU +12V rail might not have enough juice to handle both cards. Since single card won't work, it should be something else.
It is a bit tedious and troublesome but if you don't want to RMA ur mobo or the new card yet, u better use back the old board to test each graphic cards again to ensure it is the mobo problem and not the card problem.
Crunch ur parts here and find out what is the wattage required http://www.extreme.outervision.com/psucalculatorlite.jsp.
It is always better to buy the PSU that have enough connections to handle 2 cards rather then relying on molux to pci-e adapter coz of the amp issues.
What is the speed of ur ram btw ? coz some mobo ( in my case is ASUS ) is selective about the rams when it is over 1600Mhz.