getting details on system freeze:

1) Please enable NMI watchdog in the BIOS settings.

2) Add below line to sysctl.conf

kernel.unknown_nmi_panic = 1

3) Append nmi_watchdog=1 to kernel command line

title Red Hat Enterprise Linux Server (2.6.18-128.el5)

        root (hd0,0)

        kernel /vmlinuz-2.6.18-128.el5 ro root=/dev/sda nmi_watchdog=1

        initrd /initrd-2.6.18-128.el5.img

4) Enable kdump

5) Try to get the crash logs from netconsole or serial console.