Start by checking for disk full or corrupt filesystem.
If your console is usable (e.g., using the grub editor to add <space>3 to the end of the kernel command-line, you should be able to check space (note that df is not useful on btrfs (and really should warn users who run df on a btrfs filsystem) and also do a safe shutdown or restart.
If console is not usable, you can boot a Live Installer, mount the system root drive (e.g., with Gnome Disks) and check for filesystem problems.
If the root filesystem is OK, please provide the output from running inxi -Fzxx in a terminal (if you are using a “Live” environment, you may have to install inxi) so we can understand your hardware.