Hi Bud
2 reasons that could be does the theme come up looking like a basic version if so you probably dont have the windows 7 theme files patched to allow 3rd party themes they would still just be locked to the microsoft ones. Grab the instructions from the link in the post above to get universal theme patcher to patch your windows 7 theme files after patching reapply the theme and you will be good to go
The other reason would be that your graphics card cannot handle aero I am sure u would know that though if was the case so the first option would be the reason why