Not able to get past login screen

I recently installed CentOS. The installation was smooth but on booting (the very first time) I am not able to get past the login screen. If the password is incorrect, it mentions "authorization failure". But if it is correct the login screen disappears for a second but returns to ask for login again. It is a login recycling. I also tried control-alt-F1 and F2 etc. I get a terminal but there also the login is coming back every time. It happens even if I try to login as root. I have not been able to login to this newly installed distro even once, though I can access it through another distro installed on the same computer. Any help will be appreciated.

Have you tried chrooting to that install from the other one? I installed debian from within an already running distro, and the guide skips the step where you set a root password. And a few other admin steps that actual installers normally handle for you. So you could chroot to that distro and run `passwd` as root to set a root password. And then see if you can login with the new password.

The password is correct. It is not a password problem.

I changed the password but still it is returning to login screen immediately (both in gui and in terminal).

Have you checked the /var/log/ elements from the other distro for that one to see if there's any hints as to why it does what it does?

Normally when I get things like that I start questioning hardware. A spot on the disk that didn't write what it was supposed to write? Bad ram that causes random behavior and other things. Did the install go flawlessly? No power blinks or overheating influences? Integrity checks of the storage medium before installation? It could be any one of a thousand different things or a combination of them. And unless you happen upon the one thing that fixes the issue you'll never really know for sure. Most times it's just faster to do the install again than to troubleshoot the issue.

Are we talking something old or with relatively low available RAM? Without swap it is possible to trigger the kernels defenses even during an install. Not everything plays that well in confined spaces these days.

var/log/messages and Xorg.0.log are large files. The system is fairly recent with one Tb hard disk, 4gb RAM and nvidia graphics card. I see nouveau in log files. Swap is there on the hard disk. Installation was uneventful.

Odd , did you by chance pick and choose what programs to install
as in remove some default programs and add other non-default programs

that can mess up the anaconda installer

if so

Then do a new install with the default desktop

Check the source cd or dvd for defects. That alone may not prove it will work on your system.

Get a new disk and try a new install. Burn the disk at the very slowest speed and use high quality disk.

Sounds to me like the password is correct and the user account logs in, but is immediately kicked back out again. Is this a graphical or text based login? If graphical, try logging the user in from a text based console (Ctrl+Alt+F1) and see if any error messages are displayed. If this is a text based login, check what shell the user has in /etc/passwd (last field of the /etc/passwd line for that user account).

The system boots normally till login screen. It is graphical login. However, on going to terminal (control-alt-F2) the same problem is repeated: as soon as the password is entered, it immediately clears the screen and returns to login prompt. If incorrect password is entered, then error message is displayed, otherwise there is no error message.

The shell is /bin/bash, both for root and for user.