Linux Crash

Hi, all,

Our Redhat linux server crashed, and I had to cold rebooted it.
when booting up, manual fsck was required.

# uname -a
Linux 1sg 2.4.7-10 #1 Thu Sep 6 17:27:27 EDT 2001 i686 unknown

# last | grep crash
iSM pts/0 172.28.11.30 Wed Jul 21 14:56 - crash (01:23)

in /var/log/message, before Jul 21 14:56, there is the following info

Jul 21 14:55:15 1sg login(pam_unix)[2773]: session closed for user submanager
Jul 21 14:56:40 1sg login(pam_unix)[3023]: session opened for user iSM by (uid=0
)
Jul 21 14:56:40 1sg -- iSM[3023]: LOGIN ON pts/0 BY iSM FROM 172.28.11.30
Jul 21 16:20:30 1sg syslogd 1.4.1: restart.

Why our server crashed? Any tips will be appreciated.