I had the same problem, it ended up being a problem with the registry. Mine would take forever to shut down.
Windows has to reference the registry every time it shuts down or starts up. If you have corrupted files it will try to look for programs that are no longer there, orphaned or corrupted registry files will cause your pc to freeze or slow to a snails pace.
You need to clean and repair your registry. A lot more info here on registry repair and a list of programs you can use, they are not free but well worth the investment. http://registry-repair-program-reviews.com
