I'm assuming that you've checked for the obvious, e.g.
installing off a badly burnt DVD.
This message implies that you have a problem with the TTY program that is being used to handle the logins; usually, mingetty
Since you can't log in, the first thing to do is to boot up into single-user mode by adding the kernel command-line option “s” when you boot up. (Search LQ for instructions on how to do this).
If that doesn't work then you'll need to boot off a rescue disk to get your install to work; most distro DVDs support a rescue option, often using the “rescue” keyword. Alternatively, you can download a dedicated rescue system from www.distrowatch.org.
The next thing to do is to run a filesystem check. Your *getty program is broken, which means that a file in it must have become corrupt; fsck will find this and might even fix it:
If you get errors about filesystems being mounted read/write then you can remount them as read-only using:
mount /path/ -o remount,ro
If that doesn't fix it, then you will have to reinstall your getty and mingetty packages.
Hope that helps,
— Robert J. Lee