You need to edit the slim.conf file and your .xinitrc file.
vim /etc/slim.conf ( as root / sudo)
Then scroll down to the section that shows default user & uncoment & add the name of the user. Then change login_cmd as shown below.
# default user, leave blank or remove this line
# for avoid pre-loading the username.
login_cmd exec /bin/bash -login ~/.xinitrc %session
You then have to make sure your /home/user/.xinitrc file includes this line-->
exec startxfce4 --with-ck-launch