In one x terminal, monitor your log real time
[phil@uilleann phil]$ su -
[root@uilleann root]# tail -f /var/log/messages
Mount a cd in /mnt/cdrom1 and see if you can spot something before it locks.
I used Redhat 9.0 for 3 days and went back to 7.3. It would be locked up when I woke up in the mornings and I never could find out what it was.