For what it's worth, I went in to our lab and hooked up an X850 to the Gateway FPD2185W and was able to connect with both VGA and DVI.
One thought might be to uninstall the ATI driver and see if the system at least comes up using the Windows VGA driver. Set the resolution to a common resoltuion, say 1024 x 768, and then reinstall the ATI drivers.
Darv
Portrait Displays
http://www.portrait.com