Background

After packages update, use poweroff to shutdown the machine normally.
Change the memory stickers and disk stickers of the machine, and reboot the machine.
The sddm screen is black.

Observation

When power on, my laptop boots into the operating system, and running /usr/lib/Xorg in tty2.
The screen is black, with an underline on left-top, not blinking.
I can switch to tty1 and tty3 using ctrl + alt + f1/f3.
I can login into tty3 as root user, and issue commands.
In tty3, I can see only /usr/bin/Xorg and /usr/bin/sddm-greater is running.
Using journalctl -b | grep sddm, the sddm-greater says it fails it fails to authticate with pam. (Though this is not the real reason, the failure of graphics cause the faillure of pam)
The network and bluetooth works in tty3.

Attempts

• Try to update the packages using pacman -Syu.
• Try to re-install pam, pambase and sddm.
• Try to modify the nvidia parameters for kernel.

Solution

Boot into bios and toggle the graphics settings to only use discrete GPU. (It looks like there is some bugs in ASUS hardware. In hybrid mode, the GPU switch is controlled by the power and the phase of booting.)
Don’t use nvidia-settings to generate the Xorg configuration file, just delete the /etc/X11/xorg.conf file.