REGEDIT->HKEY_CURRENT_USER->SOFTWARE->MICROSOFT->
WINDOWS->POLICIES->EXPLORERThen go to right side and by right click of your mouse create new DWORD value with name NoClose and after creating click on it and give Value Data 1.
And Reboot your pc ..now your Turn Off option is disabled ..to Enable it again ..go to that directory by regedit ..and simply delete that created NoClose and Log Off Your User and Log in again ..your Turn off Again Working.