After an upgrade on Manjaro, I got no graphical environment. Looking in the logs it tells me something is going on with nvidia:

$ sudo journalctl -b
...
Jan 25 19:11:53 detective systemd-modules-load[345]: Failed to find module 'nvidia'
Jan 25 19:11:53 detective systemd-modules-load[345]: Failed to find module 'nvidia-drm'
Jan 25 19:11:53 detective systemd-modules-load[345]: Failed to find module 'nvidia-uvm'

Then trying the reinstall at a command prompt:

sudo mhwd -f -i pci video-nvidia

It complained about all kinds of kernel drivers not being found linux510-nvidia, linux513-nvidia and not being able to uninstall because of dependencies for psensor, nvidia-utils and libxnvctrl. I had to manually uninstall these, but only after I installed kernel 515rebooted and removed the old kernels. Then reinstall.

sudo mhwd-kernel -i linux515
sudo reboot
sudo mhwd-kernel -r linux513 
sudo mhwd-kernel -r linux510
sudo pacman -R psensor nvidia-utils libxnvctrl
sudo mhwd -f -i pci video-nvidia

In actual fact, I got graphics back after the reboot, but I figured I best tidy up.

Related to: Manjaro Gnome Failure After Update