Windows 7 not loading aero effect?

i had my computer for a while and it came with windows xp. about a year ago i updated it with windows 7 ultimate and everything was working fine, i had the aero effect on and everything. just last week i got a bad virus and i wiped my hhd and reinstalled windows 7 ultimate. it is activated and everything but now the aero effect wont work and i tried troubleshooting and it said my video card does not support aero. how can it not support aero if i had it just 2 weeks ago before i reinstalled windows 7? when i right click desktop and click personalize, i click 1 of the aero themes but the only thing that changes is the desktop wallpaper. the theme does not change to aero and it is stuck on basic. i also tried every possible fix for it from trying to update my drivers to forcing it to enable with the regedit and still it doesnt work. can anyone please help me with this?|||why do you have 3 of the same question? get a new video card