https://wiki.archlinux.org/index.php/xorg

Try pressing Ctrl+Alt+F2 (Host+F2 in vbox) to switch to another virtual terminal.
Then do a text login.

Then you can query what the problem is, for example in .local/share/xorg/Xorg.0.log

https://forum.manjaro.org/t/xorg-still-broken-in-virtualbox-after-update-2016-05-22-stable/1999/3
etc/X11/xorg.conf.d/90-mhwd.conf

#Section "Device"
#      Identifier  "Device0"
#       Driver      "vboxvideo"
#EndSection

Xorg -configure
/var/log/Xorg.0.log

startx

/etc/modules-load.d/virtualbox.conf

vboxguest
vboxsf
vboxvideo

group/xorg-apps

forwarding
https://ostechnix.com/how-to-configure-x11-forwarding-using-ssh-in-linux/