To shut down, restart, log off or lock your computer in C#.

First, add this using namespace statements:

using System.Diagnostics;
using System.Runtime.InteropServices; 

To shut down your computer, use this code:

Process.Start("shutdown","/s /t 0"); // starts the shutdown application 
                                        // the argument /s is to shut down the computer
                                        // the argument /t 0 is to tell the process that the specified operation needs to be completed after 0 seconds

To restart your computer use this code:

Process.Start("shutdown", "/r /t 0"); // the argument /r is to restart the computer

To log off, add this extern method to your class:

[DllImport("user32")]
public static extern bool ExitWindowsEx(uint uFlags, uint dwReason);

Then, to log off invoke the method: 

ExitWindowsEx(0,0);

To lock your computer, add this extern method to your class:

 [DllImport("user32")]
 public static extern void LockWorkStation();

Then, to lock, invoke the method:

LockWorkStation();