From your description, I assume you are getting
a constant stream of messages to the console
and therefore cannot login to the system.
If this is the case, You should bring the system
up in single user (maintenence) mode and first
disable the system program that is causing these
messages. For instance, some service deamon
is failing to start due to some error, you might
have to comment out an entry in /etc/inetd.conf
or somthing in the rc.d directory.At this point
you can then restart the system in multiuser
mode and troubleshoot the problem from the
command line.

It would help to "see" what messages
you are getting.