Assuming you have not altered your computer setup: Make sure all hardware is
connected and drivers are up-to-date and functioning. Rerun the performance
check at a time when the computer is idle. Close down all open windows prior
to the check.

Charlie42

The performance rating is meaningless and does nothing but confuse
people.

Is your computer slower than it used to be? Unless it is, ignore the
performance rating.

like system restore, performance rating is another useless feature of windows
vista. however, the rating that usually appears in that feature can be
altered by installing updates of your display driver, also upgrading the
display card (if any) to a card that supports aero.

after installing display driver updates - run the performance information
and tools from the control panel - then click on Update My Score. note that
the rating / score is determined by the LOWEST SubScore in the array.

yet - do not regard performance rating as reliable indicator.