Well...you don't have onboard video...so I would try removing/reseating the video card.
It helps to know the exact type of ATI card you have. Did you install the ATI drivers (actually, they normally install from XP)?
And...check all connections.
Since I have no idea what you did when installing, I cannot comment on the chances of your hurting the video card. But I will say that I've not ever experienced such and I'm pretty careless when I get to taking things out and putting them in
I have two ATI AIWs, 7500 and 9600.