Try to disable the integrated graphics on your mobo, either via BIOS or windows device manager.

1) There are two ways to do it. When you boot up, you can press a key (for me it was DEL, depends on mobo) to get into BIOS screen. In the device or peripheral setting, there should be option to turn off onboard sound and another option to turn off the intel integrated graphics. Also, you can go into Device Manager of Windows. In XP it is Control Panel -> System -> Hardware. Turn off the device from there.

2) Try turning off dual screen in display properties, means use only one monitor.

3) Read Yue's post. Check what slot is your new card put into.