Compaq s6500nx Video Card

So my friend wants to be able to play more games on her computer but I've seen that her pc has onboard graphics but an available AGP slot. I have an extra ATI Radeon 9600 that I know works since I already tested it in another pc. I've tried to change the primary graphics to AGP in the Bios yet still when the video card is installed, the pc turns on but does not boot, or give any beep codes at all, just a blank screen. It works when after I remove and and use the onboard graphics port. The psu is 250 watt which should be fine since that was what the test computer had, too. What do I do?