follow these instructions
login as user to console
pacman -Q | grep box
sudo pacman -R all your current virtualbox stuff
sudo pacman -Syy
sudo pacman -S virtualbox-guest-utils
then the most important bit;
sudo systemctl enable vboxservice
still having issues?
lsmod and check the listed modules from the arch wiki are loaded. especially vboxvideo
uninstall and try again with DKMS
sudo pacman -R virtualbox-guest-utils and see if xfce will start. if does but the window is static resolution then probably something a miss with the video. ensure you havent installed intel drivers or something as a part of a physical computer install which might be interfering.
still nothing - start digging into the logs. the error message you see will refer to a
Xorg.0.log which will be worth a look, and your dmesg for any errors with drivers on boot.
edit:removed unnecessary package.