Don't manage to turn computer off

["Rodolfo Medina" <romeomedina@libero.it>]

Hi.

I don't manage to turn off my Hyundai 255KI 15,
Debian Sarge 3.1, neither with '# shutdown -h now'
nor with '# halt'.
Any help?
Instead, I can reboot the computer with '# reboot'.
Also, I can turn it off with Mandrake 10.1 with '$ halt'.

Thanks for any help.
Rodolfo