Why won't my monitor display POST info over DVI, but does over VGA?

I figured that it was a problem with my Gateway FPD2185W monitor, so I called and they sent me a new one. However, now that the new one is here the problem persists.

Ideally I'd like the monitor to run off the DVI cable from the pc because my 360 is hooked up to the VGA input. But like I said earlier, when the monitor receives the picture from the DVI it doesn't display the POST test information. This makes it really hard to get into the BIOS to make adjustments. However, if the picture is fed to the monitor via the VGA input everything works hunky dory. Anyone have any idea why this is happening? Gateway has no idea. I use a Radeon X800 XL graphics card if that helps.

Thanks in advance,

Todd