It could be that your computer is "crashing" during shutdown.
Go to My Computer/Properties/Advanced/Startup and Recovery and remove the
check from the box "Automatically Restart.
Now if the system crashes on shutdown you will be presented with a blue
screen that "may" help others identify what may be causing the problem.
--
Regards,
Richard Urban
Microsoft MVP Windows Shell/User
Quote from George Ankner:
If you knew as much as you think you know,
You would realize that you don't know what you thought you knew!