The Shutdown method unloads programs and DLLs to the point where it is safe to turn off the computer. All file buffers are ...

The Shutdown method unloads programs and DLLs to the point where it is safe to turn off the computer. All file buffers are flushed to disk, and all running processes are stopped. On computer systems running Windows NT/2000, the calling process must have the SE_SHUTDOWN_NAME privilege.
The method returns an integer value that can be interpretted as follows: 
0 - Successful completion.
Other - For integer values other than those listed above, refer to Win32 error code documentation.