Graphics card install

This is in regards to my parents computer that I'm trying to help them with. It's a Gateway computer that has a mobo with a video driver built in, so the monitor plugs straight into the board. It also has the pci slot for a graphics card.

A few months ago they lost all their red in their monitor. After a series of trouble shoots I figured out its not the monitor or the cable but something in that "on board" video connection. I found them a decent graphics card on newegg (I'll post what type up later when I can find the box...) For a few months this fixed the problem. However recently a new problem has popped up. The monitor can't recieve a signal from the graphics card. If I plug it back into the onboard connection it works (minus the red). So as I see it there's something either wrong with the card or the pci slot for the card.

What I want to know is there anything I'm supposed to do differently when installing a graphics card on a mobo that has a built in one? Generally its unistall the old and install the new but since its a complettely different port is there somewhere I need to go to change anything to make sure it's paying attention to the card? Or am I most likly just looking at a bad card that needs replacing?

Thanks in advance,
Matt