Install OpenBox
Transfer menu.xml, rc.xml and autostart in ~/.config/openbox
Do this with normal user.
Use ls -lah ~/.config/openbox to verify:
Install pyxdg from the repo:
pacman -S pyxdg
Install xinit
pacman -S xorg-xinit
xinit is X.Org initialization program.
Install Xorg server
Xorg server is needed to start X, xinit will not work if there is no X server.
References:
cyruslab 
Not work! Run: startx Return: Fatal server error: no screens found
Hi Eduard, just install the fbdev driver or check the log file.
pacman -S xf86-video-fbdev