Are you sure that the system is not trying to install updates when the call to shutdown is executed?

It could also be a hung process waiting for an application to close before it shutsdown.

Another alternative is to right click on the task bar and select Task Manager.

See which processes are running.  From that same screen you can also click on "Shutdown" and try both of the following:

After clicking "Shutdown", try clicking "Turn Off".

If that doesn't work, click Log Off.  This usually works and then the system will shutdown by clicking Turn Off .

Sounds like a hung program application.