ManagementClass MC = new ManagementClass("Win32_OperatingSystem");
ManagementObjectCollection ObjCol = MC.GetInstances();
//there is only one object in the Collection
foreach (ManagementObject MO in ObjCol)
MO.Scope.Options.EnablePrivileges = true;
Note that if you skip the EnablePrivileges line you will get a exception with the message:
Privilege not held
This assumes the identity of the process has the privilege to shutdown the computer under normal conditions.