System shutoff 1 min after yum update

[Robert Moskowitz]

I did a yum update this morning; picked up about 20Mb of new stuff.

1:20 min later the system just up and powered off.

There is nothing in /var/log/messages between the yum update messages 
and the start messages.  ANy thoughts and what caused this?  Here is 
what I got today:

Jan 06 08:41:52 Updated: 2:gimp-libs-2.6.8-1.fc12.i686
Jan 06 08:41:55 Updated: krb5-libs-1.7-15.fc12.i686
Jan 06 08:42:28 Updated: 2:gimp-2.6.8-1.fc12.i686
Jan 06 08:42:38 Updated: devhelp-2.28.1-2.fc12.i686
Jan 06 08:42:39 Updated: 2:gimp-help-browser-2.6.8-1.fc12.i686
Jan 06 08:42:41 Updated: krb5-workstation-1.7-15.fc12.i686
Jan 06 08:42:43 Updated: krb5-devel-1.7-15.fc12.i686
Jan 06 08:42:47 Updated: gdb-7.0.1-19.fc12.i686
Jan 06 08:42:49 Updated: less-436-5.fc12.i686
Jan 06 08:42:51 Updated: psacct-6.3.2-59.fc12.i686
Jan 06 08:42:55 Updated: 2:shadow-utils-4.1.4.2-2.fc12.i686
Jan 06 08:43:23 Updated: selinux-policy-3.6.32-63.fc12.noarch