Window 7 Ultimate Aero preview does not work

Windows 7 user can preview the actual window when they hover their mouse over the application bar (at the bottom of the window). This is known as the Aero effect.

Problem:
The user can only see a rectangular box (no preview). Is my installation faulty? No.

Cause:
The Aero effect is not turn on by default for Windows 7 Ultimate edition. It depends on a window service called Desktop Window Manager Session Manager. The service is set to manual for default installation.

Resolution:
Set the "Desktop Window Manager Session Manager" start mode to "Automatic".

Step-by-step:

1. Type services.exe into the Run textbox and press enter. This will open the window service listing.
2. Locate Desktop Window Manager Session Manager service and right click on "Properties"
3. Set the start mode to Automatic.
4. For instance effect, start the service.
5. Voila.