In same session, now mouse does even less

I wrote a question earlier a few minutes ago, when I went to access my e-mail today and, for the first time, found that using the mouse to select a message (to read it on the reading pain at the bottom) didn't work.  At first, at least I was able to go to a different message by using the down and up arrow keys, but within a few minutes, even this didn't work - when I tried to use the arrow key, only the message itself went "up and down".  Normally, I would just click on another message and would "get out" of the message, and then would be able to use the up and down keys (or the mouse, by point and click) -- HOWEVER, the mouse no longer works to be able to select a message, so I can't get onto any other message, unless I go into the mode of viewing the messages one at a time.  I prefer to use the  bottom reading pane for most items (it's faster).  What's going on?  I tried signing out and signing back in again, but the same problem occurred.  I even tried re-booting.  Has something happened recently to Outlook?  Note:  There is nothing wrong with my mouse.  I am having no difficulty using it normally in other applications.