slim can not login xfce4

[fei wang]

Installed slim by the way of fedora RPM tools yum, but it couldn't
login in xfce4 desktop in the case that  I selected XFCE4 as the
default session through press F1. The login screen go back to ask
me once input username and password. It seem that slim installation
disability to configure login manager.

So, how can I figure it out manually. Thanks a lot.

-- 
Have a nice day.

Peter .wang