Why, because Nvidia renamed the 9800 to the gt230.
1. Make sure you have SLI enabled, by going to the Nvidia control panel by right clicking on the Desktop and slecting NVIDIA Control Panel.
If you don't have the Nvidia control panel installed, you are likely using drivers provided by Windows Update. In this case, skip forward to Section II.A. of this guide to install the latest drivers.
2. In the Nvidia Control Panel, click on Set SLI and PhysX configuration in the Task menu on the left side.
3. Make sure the radial button next to Enable SLI (recommended) is marked. If not, mark it, click Apply and follow the on-screen instructions.
4. When that's in Order, click on Adjust image settings with preview. Make sure Use the advanced 3D image settings is marked. If not, mark it and click Apply.
5. When that's in Order, click on Manage 3D Settings in the task menu on the left.
6. On the right side, look for an entry called SLI Performance Mode. Make sure this is set to NVIDIA recommended.
7. To check whether SLI is working in your game or not, go to the 3D Settings in the horizontal menu bar (not Manage 3D Settings in the task menu!) and make sure Show SLI Visual Indicators has a checkmark next to it. This will enable the SLI visual indicator in 3D Applications like games, which will show up as a green bar on the left side/middle of the screen and SLi written next to it if SLI is working in a 3D Application/game.
8. Close the Nvidia Control Panel.
9. Start the 3D Application/game you wish to check SLI on. If the green SLI visual indicator overlay appears on screen that says SLI, SLI is working in your game and all is good. If no indicator appears, it's not working (unless it's the PhysX indicator that comes with newer PhysX revisions, but that one says PhysX > GPU or PhysX > CPU).
The other option is to remove both cards and drivers and go again. If your first card was installed when it was a 9800 still you might need to pull it out to get the OS to spot it as the renamed 230.