If for some reason, you are unable to enable or run or start Aero feature in Vista, here are some troubleshooting steps you can try :
First, ensure that your version of Vista has Aero. Home Premium, Business & Ultimate have Aero.
Also ensure that your Graphic card supports WDDM (Windows Display Driver Model)
Next, right-clicking on the desktop, select Personalize.
Click on Themes and select the default Windows Vista themes.
Next, in Windows Color & Appearance, ensure that Enable Transparency is checked.
Now, inspite of this, you still find that Aero does not work, or your Aero has stopped working, simply copy-paste the following command in Vista Start Menus Search Box, and hit Enter. rundll32.exe Dwmapi.dll,DwmEnableComposition
This will re-enable Aero by flushing it. From
VISTA TROUBLESHOOTING TIPS.