Has it ever worked on this machine?
Aero is available in the following Windows 7 versions;
Windows 7 Enterprise
Windows 7 Home Premium
Windows 7 Professional
Windows 7 Ultimate
Aero is not included in Windows 7 Home Basic or Windows 7 Starter. You can find out which edition of Windows 7 you have on your computer by opening System in Control Panel.
Aero hardware requirements
Your computer's hardware and video card must meet hardware requirements to able to display Aero graphics. Check that your computer meets the minimum hardware requirements for running Aero:
1-gigahertz (GHz) 32-bit (x86) or 64-bit (x64) processor
1 gigabyte (GB) of random access memory (RAM)
128-megabyte (MB) graphics card
Aero also requires a DirectX 9 class graphics processor that supports a Windows Display Driver Model Driver, Pixel Shader 2.0 in hardware, and 32 bits per pixel.
For best results, you might also want to follow these graphics processor recommendations:
64 MB of graphics memory to support a single monitor with a resolution that is less than 1,310,720 pixels (for example, a 17-inch flat panel LCD monitor that has a 1280 x 1024 resolution)
128 MB of graphics memory to support a single monitor with a resolution from 1,310,720 to 2,304,000 pixels (for example, a 21.1-inch flat panel LCD monitor that has up to a 1600 x 1200 resolution)
256 MB of graphics memory to support a single monitor with a resolution greater than 2,304,000 pixels (for example, a 30-inch wide-screen flat panel LCD monitor that has up to a 2560 x 1600 resolution)
I have the icon and also tried the windows key + tab.