I'm having the same difficulty with my Quadro CX, however I'm running a dual-boot machine with both Vista 64 and XP 64. After my initial installation of the Quadro CX card and its latest Nvidia
drivers, I did get a signal through the DisplayPort and its DVI adapter to my second monitor. But then the signal dropped out and returned only a couple times (after uninstalling and reinstalling
drivers, cables and the card itself). Now nothing I try gives me a signal from the DisplayPort to my second monitor.
I am on the verge of purchasing either a Dell or HP monitor with DisplayPort input in hopes that a direct connection from the Quadro to a monitor (not using a DisplayPort-DVI adapter) will yield success. But I hate to invest a couple thousand dollars in a monitor only to discover that the problem lies with the Quadro card itself.
If anyone has evidence that the Quadro or the DisplayPort-DVI adapter is at fault, I'd really appreciate hearing from you.