LinuxQuestions.org - system reboot its self after a interval

Hi

Linux system is rebooted by itself after a interval.

system log is...
[root@localhost~]# last reboot
reboot system boot 2.6.18-8.el5 Mon Oct 14 22:00 (00:51)
reboot system boot 2.6.18-8.el5 Mon Oct 14 21:21 (01:30)
reboot system boot 2.6.18-8.el5 Mon Oct 14 20:40 (02:11)
reboot system boot 2.6.18-8.el5 Mon Oct 14 20:24 (02:27)
reboot system boot 2.6.18-8.el5 Mon Oct 14 20:15 (02:36)
reboot system boot 2.6.18-8.el5 Mon Oct 14 20:10 (02:41)
reboot system boot 2.6.18-8.el5 Mon Oct 14 20:04 (02:47)
reboot system boot 2.6.18-8.el5 Mon Oct 14 19:57 (02:54)
reboot system boot 2.6.18-8.el5 Mon Oct 14 19:43 (03:08)
reboot system boot 2.6.18-8.el5 Mon Oct 14 19:35 (03:15)
reboot system boot 2.6.18-8.el5 Mon Oct 14 19:24 (03:27)
reboot system boot 2.6.18-8.el5 Mon Oct 14 19:19 (03:32)
reboot system boot 2.6.18-8.el5 Mon Oct 14 18:52 (03:59)
reboot system boot 2.6.18-8.el5 Mon Oct 14 18:46 (04:04)
reboot system boot 2.6.18-8.el5 Mon Oct 14 18:27 (04:24)
reboot system boot 2.6.18-8.el5 Mon Oct 14 18:11 (04:40)
reboot system boot 2.6.18-8.el5 Sun Oct 13 22:56 (23:55)
reboot system boot 2.6.18-8.el5 Sun Oct 13 22:53 (23:58)
reboot system boot 2.6.18-8.el5 Sun Oct 13 22:37 (1+00:13)
reboot system boot 2.6.18-8.el5 Sun Oct 13 22:09 (1+00:42)
reboot system boot 2.6.18-8.el5 Sun Oct 13 22:00 (1+00:51)
reboot system boot 2.6.18-8.el5 Sun Oct 13 21:56 (1+00:55)
reboot system boot 2.6.18-8.el5 Sun Oct 13 21:50 (1+01:01)
reboot system boot 2.6.18-8.el5 Sun Oct 13 21:45 (1+01:06)
reboot system boot 2.6.18-8.el5 Sun Oct 13 21:38 (1+01:12)
reboot system boot 2.6.18-8.el5 Sun Oct 13 21:34 (1+01:17)
reboot system boot 2.6.18-8.el5 Sun Oct 13 21:30 (1+01:21)
reboot system boot 2.6.18-8.el5 Sun Oct 13 21:26 (1+01:25)
reboot system boot 2.6.18-8.el5 Sun Oct 13 21:22 (1+01:29)
reboot system boot 2.6.18-8.el5 Sun Oct 13 21:17 (1+01:33)
reboot system boot 2.6.18-8.el5 Sun Oct 13 21:13 (1+01:38)
reboot system boot 2.6.18-8.el5 Sun Oct 13 20:57 (1+01:54)
reboot system boot 2.6.18-8.el5 Sun Oct 13 20:42 (1+02:08)
reboot system boot 2.6.18-8.el5 Tue Oct 8 15:55 (6+06:56)

wtmp begins Tue Oct 1 20:38:55 2013

[root@localhost ~]# uptime
22:56:05 up 56 min, 2 users, load average: 1.11, 1.04, 0.77

root@localhost ~]# less /var/log/dmesg
scsi2 : ahci
ata3: SATA link down (SStatus 0 SControl 300)
scsi3 : ahci
ata4: SATA link down (SStatus 0 SControl 300)
scsi4 : ahci
ata5: SATA link down (SStatus 0 SControl 0)
scsi5 : ahci
ata6: SATA link down (SStatus 0 SControl 0)
Vendor: ATA Model: WDC WD3200AAJS-6 Rev: 03.0
Type: Direct-Access ANSI SCSI revision: 05
SCSI device sda: 625142448 512-byte hdwr sectors (320073 MB)
sda: Write Protect is off
sda: Mode Sense: 00 3a 00 00
SCSI device sda: drive cache: write back
SCSI device sda: 625142448 512-byte hdwr sectors (320073 MB)
sda: Write Protect is off
sda: Mode Sense: 00 3a 00 00
SCSI device sda: drive cache: write back
sda: sda1 sda2 sda3 sda4 < sda5 >
sd 0:0:0:0: Attached scsi disk sda
EXT3-fs: INFO: recovery required on readonly filesystem.
EXT3-fs: write access will be enabled during recovery.
kjournald starting. Commit interval 5 seconds
EXT3-fs: recovery complete.
EXT3-fs: mounted filesystem with ordered data mode.
SELinux: Disabled at runtime.
SELinux: Unregistering netfilter hooks
audit(1381768182.423:2): selinux=0 auid=4294967295
input: PC Speaker as /class/input/input0
e1000e: Intel(R) PRO/1000 Network Driver - 1.1.19-NAPI
e1000e: Copyright(c) 1999 - 2010 Intel Corporation.
PCI: Setting latency timer of device 0000:00:19.0 to 64
0000:00:19.0: eth0: (PCI Express:2.5GB/s:Width x1) 00:23:24:1f:26:4e
0000:00:19.0: eth0: Intel(R) PRO/1000 Network Connection
0000:00:19.0: eth0: MAC: 9, PHY: 8, PBA No: ffffff-0ff
sd 0:0:0:0: Attached scsi generic sg0 type 0
floppy0: no floppy controllers found
lp: driver loaded but no devices found
NET: Registered protocol family 10
lo: Disabled Privacy Extensions
IPv6 over IPv4 tunneling driver
mtrr: no more MTRRs available
mtrr: no more MTRRs available
mtrr: no more MTRRs available
mtrr: no more MTRRs available
mtrr: no more MTRRs available
mtrr: no more MTRRs available
md: Autodetecting RAID arrays.
md: autorun ...
md: ... autorun DONE.
device-mapper: ioctl: 4.11.0-ioctl (2006-09-14) initialised: dm-devel@redhat.com
EXT3 FS on sda3, internal journal
kjournald starting. Commit interval 5 seconds
EXT3 FS on sda1, internal journal
EXT3-fs: mounted filesystem with ordered data mode.
kjournald starting. Commit interval 5 seconds
EXT3 FS on sda2, internal journal
EXT3-fs: mounted filesystem with ordered data mode.
Adding 2096440k swap on /dev/sda5. Priority:-1 extents:1 across:2096440k
(END)

can any one have idea what is wrong with this server?
thanks in advance