Cannot shut down computer due to app not responding
You can take one of the 2 approaches one-by-one:

1) Command + Option + Escape brings up a window to force quit running apps.

2) In Terminal window, get the process_id by running ps -a and execute kill -9 &lt;process_id&gt; for the matching process.

If this doesn't work, quit all the other apps you can, make one last backup to time machine or equivalent and then kill all your user processes. 

kill -9 -1


You can try the above several times by reopening terminal and as a last resort, pressing and holding the power button will force the system to a harder shutdown by pulling all power.