Geforce 5500 fx for agp ultra screen flickers

Question

i fix nvidia video card in agp. then insert the monitor display adapter in thenvidia vga out. i go to bios and set to use agp ultra. save the settings and restart. all goes fine till the logon screen. the logon screen start fliker. the the display is between recognizable and unrecognizable. i didnot install the onboard vga driver.