New video card not detected.

Hello, I need some help. A few months ago my nvidia geforce 9800 gt video card died on me. As a result, my computer automatically switched to it's pre-installed graphics card chip on the motherboard. So today I finally got a used EVGA 9800gt Video card and installed it into my computer. However, when i started up my computer the hardware wasn't detected. System shows that I'm still using my motherboards Graphic card. I tried to download and install the most recent drivers from evga website, but when I tried to install the new drivers I got a message saying"The graphics driver could not find compatible graphics hardware". I should note that I don't have the drivers CD since the new graphic card I got was used. Also, the fan from the EVGA video card is working, and the noise the card makes is there as well. So clearly the graphic card is working but not detected. Now I have no idea what to do.

Please help me!
Thank you.


SIDE NOTE, MY COMP SPECS:

2008 Gateway FX 4710
Intel Core 2 Quad Q9300 @ 2.50GHz
6.00 GB Dual-Channel DDR2 @ 332MHz
Gateway G33M05G1 (Socket 775)
512MB GeForce 9800 GT ---------> (that died, so now a EVGA 512MB Geforce 9800GT)

Check your system BIOS is one thought, perhaps the earlier failure turned off the add-on video. Some BIOS have settings for this.

I actually checked my bios but there is no option of relevance for my video card. The closest thing was chipset function in the bios but It doesn't let me change anything in there it's locked so to speak.

just replace your video card to another computer and make sure it is working properly,then connect it to your computer and go to BIOS and configured it.