If the card is powered on, and the fan is running, it just means its getting power.

It sounds like it still wants to pull off your on-board display for the video, and is ignoring the card. Also the card could be broken, but I doubt that.

They'd probably need to know your motherboard model number to tell you where to disable onboard graphics. The bios is a "dangerous" place to play around, and the wrong setting = new motherboard.

However if you feel like being risky, you basically would have to press F2, delete key, or maybe F10, depending on the motherboard manufactorer at the startup of your computer(very first screen when you restart/power on)

However from there, the place to disable the onboard video or set the video at bootup to be the agp or pci slot will vary by motherboard and bios version, but usually just vary by motherboard.