There are a few simple steps that you can undertake in order to fix this problem, which are listed below.

1. Try waiting for 5 Minutes in order for your computer to shutdown. This is because your computer must go through all open files and close them one by one.
    
2. If after 5 Minutes and you are staring at the same screen, make sure you look in your Dock and check that there aren't any icons bouncing up and down. Application such as Word  and PowerPoint  will require you to either save or discard any open documents.
3. You can try and Force Quit any open applications, this is done through the following steps.
   1. Press Command (⌘) + Option + Esc.
       
   2. Click the Application you would like to quit and press Force Quit.
      
       
   3. Click Force Quit.
      
       
4. If your computer is still not shutting down you can try Forcing it to Shut Down, by holding down the power button. This is not entirely recommended and should Only be used as a Last Resort. Doing this can cause files to become corrupted. If you are having to Force your computer to Shut Down quite frequently, then you should come and see 1Degree.