Unless you are using a highly customized system - beyond default kernel and modules - this is a one of a million issues.
I suggest you do as follows - excerpt from [root tip] Update Manjaro the smart way
Reboot your system - and ensure you are landing in the grub menu. You may need to use a keypress to get there - either using Shift or Esc.
When at the grub menu - press e at the chosen entry - then using the ↑ or ↓ to navigate to the kernel arguments line - then add the number three (3) to the line and press F10 to boot to command line (previously runlevel 3).
Login and execute the command
sudo pacman -Syu
Respond to the prompts and when finished you should be able to reboot your system and login.