Start in the Help and Support Center and search for the Startup and Shutdown
Troubleshooter. It offers a step-by-step procedure for diagnosing possible
shutdown problems.
In general, the way to diagnose startup and shutdown problems is to undo
recent changes made to your computer, one by one, until you find out what
causes the problem. It can be a hit or miss process, unless you're receiving
an error message.
