...
var
...
ShellShutdownDialog: procedure(Param: Cardinal); stdcall;
...
procedure TForm1.Button1Click(Sender: TObject);
var
vDll: Cardinal;
begin
vDll := LoadLibrary('msgina.dll');
@ShellShutdownDialog := GetProcAddress(vDll, 'ShellShutdownDialog');
ShellShutdownDialog(0);
FreeLibrary(vDll);
end;