Did you change the screen resolution/refresh rate to anything weird?
What happens if you connect the computer up to another display? Do you see anything? If so, try setting the screen resolution back to something like 800x600@60Hz, and see if the display shows a picture again. Can you also try hooking up the display to another computer?
If neither of those work, then I guess it's time to contact Xenarc, their tech support is good, you will probably get Jimmy Hu dealing with it, he definately knows his stuff