My RHEL 5.5 rebooted unexpectedly

Hi,

Please help me to resolve this issue.

Apr 11 21:16:36 Hostname syslogd 1.4.1: restart.
Apr 11 21:24:02 Hostname syslogd 1.4.1: restart.
Apr 11 22:28:09 Hostname syslogd 1.4.1: restart.
Apr 11 23:42:20 Hostname syslogd 1.4.1: restart.
 

Apr 11 21:16:36 Hostname syslogd 1.4.1: restart.
Apr 11 21:16:36 Hostname kernel: klogd 1.4.1, log source = /proc/kmsg started.
Apr 11 21:16:36 Hostname kernel: Linux version 2.6.18-194.el5 (mockbuild@x86-005.build.bos.redhat.com) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-4
8)) #1 SMP Tue Mar 16 21:52:39 EDT 2010
Apr 11 21:16:36 Hostname kernel: Command line: ro root=/dev/VolGroup00/LogVol00 rhgb quiet
Apr 11 21:16:36 Hostname kernel: BIOS-provided physical RAM map: