acpi_power_off -> no shutdown

[Rodney Schuler]

I have a system running a tyan S2080 motherboard with the latest BIOS.
 When I shutdown this system it goes through what appears to my
inexperienced eye to be a normal shutdown sequence with the last four
lines

md: stopping all md devices.
Shutdown: hda
Power down.
acpi_power_off called

I hear the hard drive power down, but the CPU cooler and power supply
remain running.  I have to hold the power button for ~5 sec to get a
complete shutdown.

I am new to linux and ubuntu.  Any suggestions on what setting I need
to tweak to get a correct shutdown and power off?