Ugh. Dell Optiplex 780 won't display w/new graphics card, works fine w/old graphics card. [View all]

Unfortunately, I've never known that much about graphics cards, and Googling leads to thousands of partial matches which don't relate to my problem. I'm hoping someone here can at least give me a hint.

I can run the nVidia Quadro K2200 just fine on my (newer) LeNovo IdeaStation, but on the Dell it just boots to monitor off -- not even black screen -- the monitor just never comes on. I have used this same Dell with an older card (nVidia GeForce GT520, IIRC) with no problems -- no need to install drivers, update BIOS, whatever. Is there some reason why this older platform is just not compatible with the new graphics card ? Or is there some kind of firmware update for the card (the Dell BIOS is current)?

(The K2200 has connectors for DVI-I Dual Link (24+5) and HDMI. None of my monitors has sockets for all 24+5 pins, so I've had to use an adapter that converts DVI-A or DVI-D (single link) to VGA. Both work fine when the card is in the LeNovo, but the monitor stays off when it is in the Dell!)