Q: messages not responding to left click of mouse or trackpad

Messages (the only app I presently am aware is affected) stopped responding to left clicks on the magic mouse, or, wireless trackpad. I can right click and the drop down menu will appear, however, I cannot make selections with the left click function--at all.

This is a screenshot of my system. Everything was working properly until 13 AUG 2016. I have rebooted several times without success. I have to "force quit" to exit Messages, selecting "Quit" will not work.

Does anybody have a solution, or has anyone experienced this themselves?