You receive an error message when launching Disk Defragmenter:

“The Disk Defragmenter is not installed on your computer”

1. Click START–>RUN and type REGEDIT

2. Click the plus sign next to HKEY_CURRENT_USER
then SOFTWARE
then Microsoft
then Windows
then CurrentVersion
then Explorer
then MyComputer
then DefragPath

In the right-pane, double-click (default) and set its data as follows:

%systemroot%\system32\dfrgui.exe

You should now be able to launch Disk Defargmeter.