This is a variation on a theme, but no solutions offered in the other threads I've read have solved the problem.
I have loaded RedHat 7.3 on an AMD XP1500+ system. I let RedHat do the partitioning.
At level 3, I cannot log in using any account, including root. I enter the user name and password and am asked again for the login:
At level 5, I can log into KDE as root, but nothing else. I get the "Login failed" message. I've tried dropping and adding users and even creating new users, but the behavior does not change.