[CentOS] Shutdown/poweroff does not power off machine

> I've got a Dell Optiplex GX240 I am running CentOS 5.4
> (kernel 2.6.18-164.9.1.el5.centos.plus)...  When I had Fedora 11 and 12 on
> it, I could issue a poweroff command and the machine would power itself
> off.
> However, under CentOS it doesn't turn the machine off whatsoever.  When it
> completes, the machine is still running with a message of "system halted."
> Then I have to physically hit the power button to turn it off...  I
> believe at some point I did try to issue a shutdown command - but had the
> same results...
>
> Anyone have any recommendations or suggestions?
>

Must be the Optiplex - Thursday afternoon, we just did poweroffs on well
over 100 servers (HVAC maintenance this past Sat!), and it worked just
fine.

       mark