I have a brand new Sapphire Radeon 7950, with 3Gbs of VRam, two Mini DisplayPort outputs, one DVI output, and one HDMI output. I have 3 screens with HDMI, VGA, and DVI input. I am able to get 2 screens to work, but I'm unable to get the one connected via Mini DisplayPort.
The one that always doesn't work has a Mini DisplayPort to Displayport converter, onto which an active displayport to DVI converter is placed.
Ah... Turns out a few pins were bent in the Mini DisplayPort adapter. If anybody comes across this problem, make sure all the pins are flat against the walls of the port. I'm hoping Sapphire will replace it, otherwise I'm going to buy a new one from here