U3011 Monitor connection problem ?

Hi everyone,

I have a short question. I just bought three Dell U3011 30" monitors and I have connected them to my computer via the DVI ports. I wanted to use the Display ports but when i connect any of them to the Displayport on either of my graphic cards, there are no connection. I have one nVidia Quadro 4000 and one Geforce GFX 590 both with many Display ports. But i can't get any one of them to connect when using the Display port. I used the included display cable and just connected one end to the monitor and the other end to the graphic card. Nothing? And when using DVI ports, everything works. But I want to use the Display ports because the Quadro only have one DVI port and I need to connect two monitors to the Quadro 4000 where right now I have one connected to the Quadro 4000 (DVI) and the 2 other monitors connected to the Geforce 590 (DVI). I can't figure out why they doesn't work with the Display cables/ports? I'm using Windows 8 Pro 64 bit in a totally new build Workstation i7 Extreme CPU. Please i need help ASAP to finish some work i have. I hope someone can help me here.

Thanks alot everyone.