The Reboot method shuts down the computer system, then restarts it. On computers running Windows NT/2000, the calling process ...

The Reboot method shuts down the computer system, then restarts it. On computers 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.