Q: My IMac can't shut down!!!

I can't shut down my 27" IMac (2012), OS El Capitan 10.11.6. I have tried every trick in the book - the only thing that works is holding down the powebutton. If I try to shut it down using the apple menu it just shuts down my desktop - but finder still won't shut down! I do backups with an external harddrive and time machine. I have also had some trubble with my bluetooth settings that also refuses to shut down. Some help please!!!