Basically in redhat we will have root login as well as user login.For security reasons we can restrict the root login in gnome mode.
For this we can do some changes in configuration files.
Steps to follow
1.search the file gdm.conf
2.Most probably it will be in /etc/X11/gdm
3.Serach for the AllowRoot in gdm.conf at first it will be like AllowRoot=true
4.Now change AllowRoot=false
5.Now save it and restart ur machine.
6.Now u can restrict the root login in gnome mode
7.It will the message The system administrator is not allowed to login from this screen