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#1231
Do you hve any transparency? preview in the task bar, snap in when you drag a window near top or sides? if you have turned all these off then aero could still be running just not showing it's features.
Sorry to hear your scores have dropped, if you have installed new video drivers they should be from ATI website, I know you have Windows 7 x64 so be sure drivers are correct. If Windows installed drivers then you may no get the ful power of your graphics card. Right click on the desktop to see if ATI Catalyst is still working. Also if ATI CCC is running, have a lok under the3D settings to see if defaults have been restored, Then turn everything back to "Performance".