Da TechArena :
Click Start, type
%SYSTEMROOT%\Performance\WinSat\DataStore
in the "Start Search" box, and then press ENTER:Delete all the .xml files in the folder.
Click Start, type performance information and tools in the Start Search box, and then click Performance Information and Tools in the Programs list.
If the following information appears, click Refresh Now to update the Windows Experience Index:
"Your Windows Experience Index needs to be refreshed.
If you are prompted for an administrator password or confirmation, type the password or click Continue.
Windows Experience Index assesses the components in the computer.
Note the value that appears next to Your computer has a Windows Experience Index base score of.
Click Update my score.