The 5870-card has two DVI's and one MDP, and I'm using Apples own adapter (I have two of them, tried both). Only by connecting to the one MDP slot, the monitor gets recognized.
On my new 2010 hex, the 5870 has ONE DVI port and TWO MDPs. Doesn't yours?
I'm having similar trouble, except that the DVI port works, but not the MDPs. Just got 2 new Dell U2410s. They each work individually when hooked to the (one) DVI port on the 5870.
They also each work when I connect them to my 2009 MacBook Pro's MDP port via a NewerTechnology MDP to DVI adaptor.
But neither monitor works connected to the Mac Pro via the same adaptor to either MDP connector on the 5870 ... not as a single monitor, and not as a second monitor (my goal, of course, is to run both U2410s side by side, one connected to the DVI, and the other connected to one of the MDPs via adaptor).
So it seems that both MDPs on my 5870 are completely dead, whether or not another display is connected to the DVI port.
Before I call AppleCare, any advice on anything else I should test? I'd consider getting another MDP-to-DVI adaptor, but if the one I have works connecting the monitors to my MBP, I can't figure how that could be the problem.
Thanks as always.