I too need a solution to this problem. I am using Ubuntu 16.04. After boot, the cursor blinks at the password input field and then freezes; while it blinks, typing in my password does not work.
The problem occurred after the computer woke up from a suspend due to low battery. When I plugged in the charger the computer came back up and froze at the password field. After that no matter how many restarts I do the issue persists.
Lenovo Flex Pad 15, 8GB, Intel Core i5-4200U @1.60hz, 2.30hz.
These guys solved it by doing this:
Boot in Recovery Mode and Enable Networking -
apt-get install xserver-xorg-input-all
apt-get install ubuntu-desktop
apt-get install ubuntu-minimal
apt-get install xorg xserver-xorg
apt-get install xserver-xorg-input-evdev