shutdonw -h now

А разве -h должен выключать питание? Насколько помню, для выключения применяется -p. Ну, и плюс ACPI в биосе и ядре.

Попробуй еще и powerdown вместь shutdown -h now.
Точно могу сказать что на RH 7.2 halt не выключал а powerdown выключал.

Но скорее всего с ядром покапаться надо.

У меня так и работает:

samson@samson:/tmp$ zcat /proc/config.gz | grep ACPI
# Power management options (ACPI, APM)
# ACPI (Advanced Configuration and Power Interface) Support
CONFIG_ACPI=y
CONFIG_ACPI_BOOT=y
CONFIG_ACPI_INTERPRETER=y
CONFIG_ACPI_SLEEP=y
CONFIG_ACPI_SLEEP_PROC_FS=y
# CONFIG_ACPI_AC is not set
# CONFIG_ACPI_BATTERY is not set
CONFIG_ACPI_BUTTON=y
CONFIG_ACPI_VIDEO=m
CONFIG_ACPI_FAN=y
CONFIG_ACPI_PROCESSOR=y
CONFIG_ACPI_THERMAL=y
# CONFIG_ACPI_ASUS is not set
# CONFIG_ACPI_IBM is not set
# CONFIG_ACPI_TOSHIBA is not set
CONFIG_ACPI_BLACKLIST_YEAR=0
# CONFIG_ACPI_DEBUG is not set
CONFIG_ACPI_BUS=y
CONFIG_ACPI_EC=y
CONFIG_ACPI_POWER=y
CONFIG_ACPI_PCI=y
CONFIG_ACPI_SYSTEM=y
# CONFIG_SERIAL_8250_ACPI is not set


samson@samson:/tmp$ zcat /proc/config.gz | grep APM
# Power management options (ACPI, APM)
# APM (Advanced Power Management) BIOS Support
CONFIG_APM=y
# CONFIG_APM_IGNORE_USER_SUSPEND is not set
# CONFIG_APM_DO_ENABLE is not set
# CONFIG_APM_CPU_IDLE is not set
# CONFIG_APM_DISPLAY_BLANK is not set
# CONFIG_APM_RTC_IS_GMT is not set
# CONFIG_APM_ALLOW_INTS is not set
# CONFIG_APM_REAL_MODE_POWER_OFF is not set


ps: система Slackware 10.1