Today we have installed Fedora10 in my PC in Virtual Box.We were aware that by default Fedora 10 do not permit root to login in Runlevel 5. Fedora has tightened their security.We did some changes in system and tested the root authentication issue in our PC.

Steps To Authenticate root to login in GUI mode in Fedora 10

Copy the gdm file

sudo cp -prf /etc/pam.d/gdm ~/gdm.backup

Edit gdm file
Find and comment this line in file /etc/pam.d/gdm

sudo vi /etc/pam.d/gdm 

...
# auth required pam_succeed_if.so user != root quiet
...

Logoff or Restart
Logoff or restart the Desktop.

sudo init 6

Once system get booted successfully, you will see the GUI screen for login. Use the root login and password to login.