Q: green fuzzy screen dvi connection from video card

I'm at a bit of a loss. Here's the situation:

I'm  using a mid 2009 MacBook Pro 5,2 with the stock GeForce 9400 gpu.

I am connection an external monitor to the lap top, but whenever I use the DVI setting, the external screen is loaded with Green snow.

I have tried two different screens with the same results. I have tried two different DVI cables as well as two different mini display to DVI adapters.

On both screens using a pluggable USB video card with the VGA out, I get a clear picture, albeit poor because of the limitations of VGA. Here's where it gets weird tho: on the pluggable USB video card, if I take off the VGA adapter and just plug that into a DVI monitor, i get the same snow.

So, I went and looked at the system profile while the monitor was plugged into the VGA adapter and sure enough even over USB the picture is still coming from the GPU.

So I'm thinking the problem is with that hardware component.

Here I'm running up against the limits of my knowledge though. Is there a fix for this? can the chip be replaced? is that user accessible? is there another solution or troubleshooting step I should take before I decide with certainty that it's the video card?

Any suggestions or help would be great. I'm living with the poor VGA signal now, but would much prefer to get the DVI input working.

Thanks.