More info:
I uninstalled 3.10 kernel and headers. I rebooted. I reinstalled them.
The first time I rebooted into the reinstalled 3.10, I was able to log in to the LXDE desktop, start a terminal, and run "free -m". But the next command I tried to enter, the keyboard was frozen, again.
I rebooted again, and things were just as before - I could not even type into the userid box of Slim. Then I rebooted into kernel 3.9-8, and everything is good.
I am still searching all the stuff in /var/log, but I still have not found anything that appears relevant. Maybe it is freezing so fast that nothing is being logged.
Tim