Windows Display Driver Model
To resolve issues with the Windows Display Driver Model, Windows 7 features a useful wizard that can help to determine the cause.
Go to Start > Control Panel > System and Security > Find and Fix Problems. From here, choose Display Aero desktop effects. The wizard will then run through several steps that should fix the Aero themes.
If this fails to work, there is one other useful method that can force Aero to run. This would most commonly be done if your graphics hardware is up to the job but doesn’t specifically support WDDM.
To force Aero to work correctly, go to Start > and type notepad. In the resulting Notepad window, paste the following:
Windows Registry Editor Version 5.00
Save the file as aeroforce.reg and double click the icon to add the details within to the Windows 7 system registry.
By doing this, you have altered how the Windows system registry handles commands to use the Aero system - as long as your PC or laptop has the necessary hardware, Aero themes should now be available to you!