It is very useful for administrator to put system wide restriction on the system so that no user can change or edit registry.
1:open regedit from run.
2:Go or scroll down to
    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System

3:create a new DWORD value,DisableRegistryTools and set its data value to 1 for disabling and 0 to enable it    again.
4:exit from registry editor and restart the session by logging off the system.

happy hacking :-D