Freeze after login Ubuntu 18.04 [duplicate]
You need to install your graphics drivers.
On your login page, press CTRL+ALT+F2
Enter your credentials and use the below commands (if you're using Nvidia graphics card)
sudo add-apt-repository ppa:graphics-drivers/ppa
sudo apt-get update
sudo apt-get install nvidia-390
If you're using some other graphics card then use
sudo ubuntu-drivers devices
to find out your recommended driver - as suggested by Joe.