Microsoft Windows 2000, XP (XP home users read section below) and later users can remotely shutdown another computer in their network by utilizing the shutdown command. To start the GUI version of this command click Start, Run, and in the Run line type: shutdown -i and press enter. After running this command you should see a dialog window shown in the example below. As can be seen in the example above, you'll have several different options to choose from in the Remote Shutdown Dialog.  First specify the name or IP address of the computer you wish to shutdown by clicking the Add button. Next, select Shutdown and keep the Warn users of the action checked if you wish to warn the user of the shutdown before it occurs. Next, in the Shutdown Event Tracker, choose the Option you wish the Event Log to show and enter a comment.
If the remote computer you're attempting to shutdown is running Microsoft Windows Home. You'll need to enable guest remote shutdown privileges before following the above steps will work. To do this follow the below steps.

1. Download the Windows Resource Kit to the computer you're wanting to remotely shutdown.
2. Once downloaded and installed, copy the NtRights.exe file from the "Program Files\Windows Resource Kits\Tools" directory into the "Windows\System32" directory.
3. After the file has been copied open a command prompt window by clicking Start, Run, and typing cmd and pressing enter. At the prompt type the below commands exactly as you see them here (unless your Windows directory is in a different path).
   
   cd\windows\system32
   NtRights –u Guest +r SeRemoteShutdownPrivilege
   NtRights –u Guest +r SeShutdownPrivilege
4. If successful after typing each of the above two NtRights commands you should get a success message. Once this has been completed, exit the command prompt window and restart your computer.

Once the above steps have been completed, you should be able to remotely shutdown that computer from another Windows computer.
This could be caused by any of the below possibilities.

1. The domain administrator has group policies in place to prevent remote shutdown.
2. Remote administration or the $ADMIN share is disabled.
3. You're logged into an account that does not have administrative privileges.