During the course of PC cleaning I lost in System tools my defragmentation site.
Any way to easily retreave it?

Try making a shortcut there with the following data:

Name: Disk Defragmenter
Target or Location: %SystemRoot%\system32\dfrg.msc
Start In: C:\WINDOWS\system32
Shortcut key: None
Run: Normal window
Comment: Defragments your volumes so that your computer runs faster and more efficiently.

Cannot locate systemroot. every icon about defrag says it does not excist????

   It sounds like you lost more than the defragmentation link.  You can replace %SystemRoot% with C:\Windows so that the Target or Locations reads "C:\Windows\system32\dfrg.msc"