Here's the normal sequence for a dual-monitor setup:
1) When you power on, the BIOS POST display will appear on one or both monitors. This depends on the type of graphics card you have. Generally though, the POST display is on the Primary Display, though some cards will replicate that onto the other monitor so both show exactly the same thing.
2) Once the BIOS POST ends and hands over to the operating system, all displays will briefly go blank; after a short while you will see the Windows splash screen appearing, generally only on one monitor, but again some graphics cards will replicate the splash onto both monitors. If you look carefully, generally one montor actually goes black not blank.
3) Quite far into the Windows boot process, both monitors will again go black, and shortly thereafter the log-in screen will appear on one monitor. Depending on you graphics card (I don't have a 9800GX2), you might be able to see and move your mouse onto the black screen/. If both monitors sho exactly the same, then you system is not set up for true dual display but simplky an additional monitor. This can be corrected once you log in.
4) Once you enter your username and password, both screens will momentarily go black, and then the Windows Desktop should be loaded and displayed on both monitors. Quite often there is a short 100-500ms delay between activation of Display One and Display Two.
Do you actualy get to load a Windows Desktop (ie with Start menu, Task Bar, and icons)?