If you are running a standalone video card try running without the Viewsonic software use Nvidia's software, assuming it came with a load disk. It sounds as if, at some time, perhaps inadvertently a dual monitor hook up(setting) was made. BTW how are you hooking up, VGA/DVI/HDMI? HDMI or DVI are preferable but depends on your vid card/monitor capability, as you likely know.
I recently purchased a Viewsonic monitor for my computer and I'm running Win XP Pro. The day I got it, I didn't have a lot of time to switch everything out but I hooked it up to make sure it was working fine. It was and I discovered I needed a newer driver for my video card which I found the next day. After installing the Viewsonic disc and Nvidia driver I switched out the monitors yesterday evening. This morning I went to the Display Properties/ Setting screen and I noticed there are two monitors in the box. Above the box it says "Drag the monitor icons to match the physical arrangement of your monitors" I did some checking and this seems to related to having a system with dual monitors which I've never had. I also didn't see this the first night I hooked the monitor up. I'd like to know if there is some way I can get rid of this? Also the two boxes below the screen resolution are both checked and greyed out. I saw something else odd that may be related in the Device Manager. When I had my old monitor, under Monitors it would list my KDS monitor, now it says Plug and Play Monitor twice. Earlier today I deleted one of them but now it's back. I'm not sure why. I'd appreciate any suggestions.