monitor VGA to video card DVI (with adapter) works, but DVI to DVI does not

I posted a question similar to this a short time ago, but I think perhaps I was not clear enough so I thought I would post again. The only connectors on my video card (GeForce 7900 GS) are two DVI-D outputs. I have no idea why, but for some strange reason I am no longer able to connect my monitor (E228WFP) to my video card using a DVI to DVI connection. Every time I try, I get no video and the monitor appears to go to sleep (and, yes, I am selecting the monitor's DVI input). However, if I use the monitor's VGA port and connect it to the card using a VGA to DVI adapter, then, and only then, can I get a picture.

I  have tried different DVI cables to no avail. I have even gone so far as to buy a new monitor (ST2310) thinking that there was a problem with the DVI port on the old monitor. But I still get the same result with the new one going DVI to DVI. The only thing I haven't tried yet is getting a new video card but I think that might have to be my next step.