MacBook won't shut down
I can't guess what is hanging up, but I can show you how to determine where the shutdown process is hanging.

You will need to boot your mac verbosely by holding Command-V when you hear the post chime. Then open a terminal and type this command to force a shutdown.


sudo shutdown -h now


This will let you see step by step how the operating system is closing things off. Once the loginwindow closes and your normal mac graphics window disappears, you will see the verbose commands and can tell us exactly where this is hanging so it's not a guess what step is failing.