The answer is pretty simple. However, give yourself a favor. Determine your brand name's model number, goto the manufacturer's site, find out its documentation and read it. If the documentation is missing or it's a kind of vaporware, run a hardware/software disclosure utility. That will reveal configuration details, because your description is missing some pertinent info.
Another track it's asking their support. If they won't be able to help you (although the answer is pretty simple), come back and say it.
You asked suggestions, so you've got suggestions.
Trying to unweave, unwind, unravel
And piece together the past and the future,
T. S. Eliot
I recently bought a used Gateway Pentium 4, 1.2 off Ebay Real nice, but when opening the side, I noticed the monitor was plugged into a little red box. I bought a XFX GeForce 5200DX and installed it in one of the three PCI slots. I saw the fan running, but upon booting up, the green light on the screen took forever to light up and nothing but a black screen. I could hear the chimes in the background indicating the bootup process was finished. No matter which slot I tried, same thing. So I pklugged the monitor back into the little red box and the picture came right on. I insalled the drivers and all of that.
I went to the device manager and under display adapters, I see the Nvidia card listed and also the default Intel GV graphics controller. Under monitors, I see two listed, the default with the Intel and the second monitor listing my new Nvidia card. Should I chose the Nvidia card, reconnect the monitor cord to the card in the PCI slot and reboot? I don't want to screw something up and not have any picture at all. Your suggestions, please?