The Windows Experience Index is measured after installation of Windows Vista and 7 however since the system drivers are not loaded, the Windows Experience Index is lower than it should be as the systems hardware is not fully utilised without correct installation of the drivers.
Click the link "system rating is not available".
Note at this stage I would re-rate the system even a number is displayed there. Although people may not care so much for the system rating it is best to perform. Several unrated systems will revert to the Windows 7 Basic Theme even if they are capable of the Aero Interface and will not allow the user to change to the Windows 7 Theme until the system is rated.
Select rate this computer and leave it be for 5 minutes to rate it.
You should get the rating now. Here are the scores on my XPS 8300 Desktop for example: