If you mean to shutdown the local machine or Remote machine, have a look at the WMI interfaces in the system.management classes.

Hi, Royce

You have to use ExitWindowsEx API and here is example, which I use with
EWX_SHUTDOWN

 [DllImport("user32.dll", ExactSpelling=true, SetLastError=true) ]
 internal static extern bool ExitWindowsEx( int flag, int reason );

 public const int EWX_LOGOFF = 0x00000000;
 public const int EWX_SHUTDOWN = 0x00000001;
 public const int EWX_REBOOT = 0x00000002;
 public const int EWX_FORCE = 0x00000004;
 public const int EWX_POWEROFF = 0x00000008;
 public const int EWX_FORCEIFHUNG = 0x00000010;

 {
       flg=EWX_SHUTDOWN;
       ExitWindowsEx( flg, 0 );
 }

HTH
Alex