Control Panel/Personaliztion/Customize colors. You will be on the Window
Color and Appearance page. Check Enable transparency. If that is not
available your video card or driver may not be WDDM compliant.
To see if your card and driver are WDDM compliant, open Control Panel/System
and Maintenance/Get Started with Windows. This opens the Welcome Center.
In the top pane look for your video card (fourth item). If the card and
driver are right the name of the card will be followed by "(Microsoft
Corporation - WDDM)"
The other possibility is that your system administrator may have disabled
Aero.