Did you close anything that you had running before you shutdown the computer?
You might see if this tutorial
can help speed up the shutdown time for you. If not, then you can create a shutdown shortcut in this tutorial
to force a faster shutdown until you find the culprit that is not shutting down gracefully.
Before you shutdown, look in the Processes and Applications tabs in Task Manager to see if anything in there may stand out to that may be the culprit. You can test and see by killing the process or application
before shutting down to see if it shutsdown ok without it running.
Hope this helps,