Hi,

I am not able to log on to the desktop as a non-root user. It is allowing only the root user. For other users, "Authentication Failure" message is getting displayed even though the password is correct.

I tried using the su command. But I get the "Incorrect Password" message . I checked the /etc/passwd/ file for corruptions. But it is perfect..

Any idea of what the problem is and how to correct it???

Thanks in advance.

Please copy /etc/passwd~ to /etc/passwd and try again

Sounds like desktop settings are corrupt in the /home directory. Have you tried to create a new user and see if you can log in with it. If you can log into graphical as root you can probably go through administrative tasks GUI or from command line as root with command:
Jimbob would be the name of the new user, you can change it if you don't like it, kinda hard to type. You will be prompted to enter a password for the new user, accept default recommendations, log out and log in as the new user. If the new user cannot log in also, you may need to remove and reinstall your display manager.