I've got atleast 5 good guesses of what the problem is. Well, that was before you said you could actually get the picture to show a little bit.
The first thing I would try is to experiment with the video settings on your Xbox 360 menu. You could possibly have your xbox set on like 720p. Lol. That's does not work with VGA and computer screens.
Next, I would try swapping your D-link cords (physically). It could possibly be that one is defective.
My last suggestion would be to make sure your d-link settings are correct. According to what I read, it can automatically detect a computer (im guessing it checks if it has video in). So, maybe there is a way to manually detect your xbox 360 from your adapter. This would be because for some reason your d-link is not detecting a computer connected (aka your xbox).
If that doesn't work, contact your manufacturer and M$. M$'s costumer support is very friendly. Give them a call at 1-800-4-MY-XBOX