after logging in like root it ask to login again

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http://www.linuxquestions.org – i have fedora 7 server running just zimbra email server. but i forgot the password. i used a livecd ubuntu then i went to /etc/shadow i used gedit and i remove the hash between the ": :" then saved file. i reboot but i still can not logging. and it does a weird thing. i wrote root then the i hit enter when ask for the password i hit enter. then the screen clean up by it self then it ask for logging again. It does nt say that the password is wrong or any other error. also i went to single-user mode then once i m at # i wrote pas (HowTos)