Ubuntu 16.04 freezes on login screen, no keyboard or mouse working

I faced the same issue on my personal computer. It seems to come from packages of kernel 4.4.0-43 that have been released without other needed ones. See https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1633267/comments/17

First try to boot an old kernel

Holding the shift key right after starting the machine should display the grub menu. Then you should be able to choose an old kernel in "advanced options".

If you manage to start your machine this way, you're lucky : you only need to upgrade to get the missing packages :

sudo apt update && sudo apt upgrade

If you can't boot the machine at all

In this case, I managed to solve it by running the upgrade from a live-USB key, through chroot :

If your system disk is not encrypted

• start the computer on a live-USB or live-CD of the same version of Ubuntu (16.04.1)
• mount your system disk (in /mnt in this example. If you mount it from the GUI, it will probably be in /media/ubuntu/some-uid : in this case, replace /mnt with this path below)

• mount the necessary directories to allow your chroot to access the Internet :

  sudo mount --bind /sys /mnt/sys
  sudo mount --bind /dev /mnt/dev
  sudo mount --bind /proc /mnt/proc
  sudo mount --bind /run /mnt/run
  

  and, if you have a separate /boot partition : (adjust the device name)

  sudo mount /dev/sda2 /mnt/boot
  

• then start the chroot and upgrade :

  sudo chroot /mnt
  apt update
  apt upgrade
  exit
  

• and finally unmount everything and reboot (not sure it's really necessary) :

  sudo umount /mnt/sys
  sudo umount /mnt/proc
  sudo umount /mnt/dev
  sudo umount /mnt/run
  sudo umount /mnt/boot
  

If your system disk is encrypted

In this case, you first need to mount it with the same name as in your /etc/crypttab (in my case it was sda3_crypt : find yours in the first column of /etc/crypttab, on the line of your system disk) :

sudo cryptsetup luksOpen /dev/sda3 sda3_crypt
sudo mount /dev/mapper/ubuntu--vg-root /mnt

then follow the same procedure as above

I explained the complete story (in French) on my blog : https://blog.mossroy.fr/2016/10/14/ubuntu-bloque-a-la-saisie-du-mot-de-passe-de-dechiffrement-luks-a-cause-dun-kernel-4-4-0-43-incomplet/

Not a solution, but a quick fix:

I experienced the exact same thing from the update today.

My workaround is to boot the previous kernel, as described in this post from a year ago.

Access the GRUB menu by pressing shift after turning your computer on, select Advanced Options for Ubuntu and go down to the older kernel in the list (not recovery).

I experienced this issue upgrading from Xenial to Zesty. I tried the other solutions, but they didn't work for me.

Instead, when I reached the GRUB menu, I entered a recovery kernel. From there, I dropped to a root terminal, and run an apt update/upgrade, followed by the recovery system's "fix broken packages" option.

That seems to have fixed it for me. I think that, for some reason, the display server failed to finish updating, and so it was left in this half-broken state.