My machine cannot halt

A thread from Slackware forum :

What can I do to halt my machine from Linux? I use Slackware 10.1 kernel 2.4.29, as root when I write
shutdown -h now
My machine finishes everything fine, but finally appears a message like this: System Halted. But my machine is not halted. I have to push the power button to do that.
When I use Fedora, and type: shutdown -h now. Fedora halts off the machine completely and I do not have to push any button to do that.
What can I do ? I want my slackware halts off completely my machine.

Thanks!!!

To know the answer follow the link :
http://www.linuxquestions.org/questions/showthread.php?s=&threadid=336613