What just happened with the last Ubuntu update?

[MR ZenWiz]

I just ran my command line version of the software updater (because it
doesn't work on my desktop), and when the system reboots, it freezes -
hangs up everything - if I try to log in on the normal desktop.

I can log in on one of the consoles in text mode, but as soon as I try
to use the X login, it freezes and nothing brings it back.  I can't
even power it down with the normal power switch, although the restart
switch works.

I tried backing down to the previous kernel (4.4.0-62), but that does
the same thing, so I'm guessing it's something in the latest Xorg or
windows manager that broke.

I'm running Xubuntu 16.04.2 LTS with the following hardware configuration:

M/B: ASRock Z97 Pro4 S/N: 56M0XE052919
CPU: Intel i7-4790K 4GHz S/N: 35447259A3160
ram: 16GB EVGA DDR3 2400MHz (PC3-19200) 2x8G
K/b: Dell DP/N 0U4730 USB PID LZ03778D0AFH
Mou: Logitech MX3000 Cordless Desktop (laser mouse)
sds: /dev/sda Hitachi 1TB SATA-3 S/N: HQ3UNXEB
        /dev/sdb    Patriot Spark SATA-6 256GB SSD S/N: 7D4B076718DF00267932
        /dev/sdc Toshiba 2TB SATA-6 S/N: Y2P4ZHHAS TZ5
        /dev/sdd    Western Digital 2TB SATA-6 WDBGKN0020HNC-NRSN S/N:
WCC4M6VJAY0H
dvd: /dev/sr0 LG HL-DT-ST BD-RE WH14NS40 S/N: K9BDAM70413
       /dev/sr1 LG HL-DT-ST DVDRAM GH24NSB0 S/N:
vid: on-board (Xeon E3 1200 v3, i915 driver)
nic: 10/100/1G on-board
f/w: AMI BIOS P2.20 5/12/2015

Kind of urgent, since that is my main compuer and had all my goodies
on it (I have a backup, but it's not the same power and speed...).

Any suggestions or clues?

Thanks.