I have a machine with a Quadro FX 580 card (DVI and two Displayport). Attached to it are two 19" Acer screens, which are both (annoyingly) VGA. The first one works perfectly, with a DVI->VGA adaptor.
The second one doesn't work. It's got a VGA cable, which goes into a VGA->DVI converted, which then goes into a DVI->Displayport converter. Initally, I was getting 'Cable Unplugged' on the screen, and it couldn't be seen by Windows or the nVidia control panel. After swapping the VGA->DVI adaptor (which works perfectly on another machine), Windows can now see the monitor. The nVidia panel sees the model and native resolution, but I get a constant 'No Signal' error. Switching to the other Displayport makes no difference.
I suspect that the card is seeing a DVI connection plugged into it (nVididaCP shows the monitor as having a DVI connection), and it only sending out a digital signal because of this. Does anyone know of a solution (other than trying to get a Displayport->VGA adaptor), or of a way to force the card to see it as VGA?