Radeon 9800 Pro does not work

my video card doesn’t seem to work for some reason. I uninstalled the drivers because i wanted to try out a Ge force video card but, then i didn’t like it so i changed again and when i booted it up it loaded up the normal screen and said “Mode not supported”

You can’t see anything on the screen but that error of somesort that says “mode not supported”

My Specs:
P4 3.2
1 G.B. RAM
9800 Pro (doesn’t work)
Hard Drive 80 GB
Windows Xp Home Edition
Motherboard-Elitegroup PT800CE-A