can't log on without using a mouse

[Tim]

Unless I use the mouse, I can't log on to a MATE desktop.  No keypresses
that I can find will get me focus onto any gadget on the logon screen,
to select which user to log on as.  I have to grab the mouse and click
on something.

Is there some secret to this?

-- 
tim at localhost ~]$ uname -rsvp

Linux 3.14.8-200.fc20.i686 #1 SMP Mon Jun 16 22:36:56 UTC 2014 i686

All mail to my mailbox is automatically deleted, there is no point trying
to privately email me, I will only read messages posted to the public lists.

George Orwell's '1984' was supposed to be a warning against tyranny, not
a set of instructions for supposedly democratic governments.