my gateway gt5428 video card would not work so I purchased a new galaxy GeForce 8400GS and installed it. I plugged the monitor into the new video card and I still do not have a display. The monitor says no signal. HELP
Your system had integrated onboard graphics I believe, so by default your BIOS is probably not finding you new add in card and initiating it. You will likely have to enter the BIOS and find a setting to disable on-board graphics, or a similar setting to tell the BIOS during POST where to look to find your new add-in video card and initiate it first instead of the on-board integrated card. Some BIOS's simply have a setting that asks something like
"Initiate Graphic Adapter First.....................Integrated/PCI Slot/AGP Slot"
or something similar.