If you want to disable the Log Off and Turn Off Computer buttons on the Start menu.

Follow these steps:

Open the Registry Editor (Regedit.exe).
Under HKEY_CURRENT_USER Navigate to:
\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Explorer.
Right-click the Explorer key, and select New | DWORD value.
Name the value StartMenuLogoff, and press [Enter] twice to access the Edit DWORD Value dialog box.
Type 1 in the Value Data text box, and click OK.
Right-click the Explorer key, and select New | DWORD value.
Name the value NoClose, and press [Enter] twice to access the Edit DWORD Value dialog box.
Type 1 in the Value Data text box, and click OK.
Close the Registry Editor.