Cyclone iii developpment board: DVI problem

In your first post you said you're trying to output a test pattern. Is that test pattern coming in your video in port and through DDR2? If so, then break things up. Drive a test pattern directly out the DVI output and play with that until it works. No point using the video in port and DDR2 memory if you can't get the output port to work.

I'll ask again about the output timing. What are your front porch, sync width, back porch and polarity settings for HSYNC and VSYNC? How many total video lines are you putting out and how many total pixel clock cycles per video line? All of that plus the pixel clock frequency have to be correct.

Do you know how to use SignalTap? If no, then learn. Have you simulated your design? If not, then learn how to do that as well. Debugging by staring at a blank display is not going to get you very far. I don't mean to be disrespectful, but you don't seem to be trying very hard here.