The system freezes at the log-in sceen after an OS upgrade

I recently upgrade my system from Ubuntu 16.04 LTS Xenial Xerus to Ubuntu 16.10 Yakkety Yak. Everything went as it should until the very last phase of the upgrade process - the final reboot.

Since then, I am able to arrive to the log-in screen, but there the system no longer reacts to typing or mouse navigation. The clock is showing the correct time, the system is able to detect wireless networks, and also the OS version and my username are displayed correctly.

So, the question is: How can I repair the system when it freezes to the log-in screen in the start up? Do I need to run some commands through GNU GRUB > recovery mode > root? Or perhaps repair some broken packages? If so, how?

Thanks a lot for your patience and kind help in advance!

Repair Ubuntu/other distro version upgrades the clean way : reinstall

(which is probably what everyone should always do instead of using the upgrade button)

My take on "how to fix the system" especially for a newbie is to do a fresh install.

Don't fret !!!

...this is infinitely faster and easier than any other possible approach and also then what apprehensions people generally have before having done it.

As preparation : using your installation USB you'll copy you home folder to a separate partition or USB/extHardDrive.

Let's do this :

Under Ubuntu Method 1 (good for UEFI boot works on any other linux)

1. create the installation USB :
   • Simply download this.
   • Format your USB 2.0 key to FAT32 using gparted.
   • (Still in Gparted) Right click on the visualized partition and select "manage flags" tick "boot" and apply.
   • Now simply mount the iso by double clicking it (this should open it's folder).
   • CTRL-A
   • CTRL-C
   • Go into the still-mounted folder of the formatted USB 2.0 key.
   • CTRL-V

Under Ubuntu Method 2 (good for Legacy boot)

1. create the installation USB :
   • Start up the Ubuntu startup disk creator.
   • use the same iso.

Under Windows (best and simplest also adaptable both to UEFI and Legacy boot)

1. create the installation USB :
   • download rufus, the bootable usb creation app.
   • still the same iso.
   • go to the icon first and select your downloaded iso.
   • then unfold this : and select one of the UEFI options if you are booting UEFI if you don't know then it's the default which is "MBR only".
2. We now have our bootable install USB key. right? if you don't, stop here and ask me.

Now boot to this usb key on your machine if it boots straight to the installer then you'll be given the option to "try first" which you should click, otherwise you should boot to a grub (likely in the rufus approach) allowing you to choose then and there if you want to install straight up or try ubuntu without installing.

We'll now in either three of these approaches have arrived at a live ubuntu desktop (if not stop here let me know). If you're using the "copy home to local partition" rather than the "copy to USB/extHardDrive" approach, now's the time to open Gparted and create said partition or simply to do the copy if the partition or HDD is already available, otherwise have your other USB/extHardDrive on-hand.

3. copy all of home. you can do this via the graphic approach or the terminal approach.
4. pinned to the taskbar there should be this icon :

. click it to re-open the same installer you'd get in the install-only boot mode and run it to completion. the "Erase Ubuntu Xenial Xerus and Reinstall" option should work. but if you don't trust that use "something else and partition manually. UEFI boot requires an EFI partition of 550M minimum, Legacy boot does not and a single EXT4 partition with mountpoint / is enough. You can ignore the SWAP warning. if you went the "make a copy partition route" and it happens to be on your install Hard Drive or you only have one HDD remember about it and don't delete it when partitioning.

Remember to select the same name and username you had during install exactly. If you have a doubt as to which box corresponds to which and both are not the same. stop and ask me.

3. Once booted in your freshly installed new ubuntu go ahead and copy back home.