hi,
i am using fc3,and i was working in my this user account for months,but since last 3 days i cannot login to my user account and the problem can be described as this:
The system seemed to accept my password, the login prompt went away, but then it came back without logging me on. What happened?
this is my syslog for this problem:
Mar 8 03:29:50 localhost login(pam_unix)[7033]: authentication failure; logname=LOGIN uid=0 euid=0 tty=tty2 ruser= rhost= user=john
Mar 8 03:29:50 localhost login[7033]: pam_krb5[7033]: authentication fails for 'john' (john@EXAMPLE.COM): Authentication service cannot retrieve authentication info. (Cannot resolve network address for KDC in requested realm)
Mar 8 03:29:50 localhost login[7033]: pam_ldap: ldap_simple_bind Can't contact LDAP server
Mar 8 03:29:53 localhost login[7033]: FAILED LOGIN 1 FROM (null) FOR john, Authentication failure
i can log as root and startx,plz help me how i can solve this problem

Looks like a PAM module is trying to authenticate you against an ldap server, and the ldap server is not responding.

try googling for some info on PAM (I've not got a lot of real experience here so I can't help that much).
The pam system is configured under /etc/pam.d and consists of seperate files for each service, try looking for any files modified about 3 days ago (or whenever your problem started occuring).

My sshd file contains:
#%PAM-1.0
auth required pam_stack.so service=system-auth
auth required pam_nologin.so
account required pam_stack.so service=system-auth
password required pam_stack.so service=system-auth
session required pam_stack.so service=system-auth

and my xserver file contains:
#%PAM-1.0
auth sufficient pam_rootok.so
auth required pam_console.so
account required pam_permit.so

if one of these lines is referring to ldap and it shouldn't be I would comment out the line with ldap in and then try and login with your user account. However, BE CAREFUL in here. Bad things can happen. Changes in here can lock you out completely to the point where you need to rescue your os, so I would read up on pam first.

HTH

Dylan