Cant install voodoo3

Question

trying to install 3dfx voodoo3 agp in my sons pc (time amd xp 2400)motherboard is a am39l. ive installed the card,un installed old driver for on board graphics, downloaded drivers for xp, rebooted. but when i plug monitor into new card all i get is "out of range" on the display. i have now tried this 3 times with no luck. i know the card works fine as it was from my brothers pc and works well on his.... help!!!