Dell dimension 4700

Trying to install a ATI RADEON X1300 SERIES. I install the card and my old agp connection say unsupported hardware found please disconnect monitor and put in dvi connection on added video card and rebott and follow directions. Done all that and I can never get the dvi connectio or the agp to work unless I uninstall the video bd and reboot to original monitor connection and all is fine but when I reinstall the card the same message comes up ! please help