ASUS A7V400-MX mainboard - the shutdown does not work (ACPI problem?)

Hi!
I have a problem:
I have an ASUS A7V400-MX mainboard, a Sempron 2300+ and a Fedora Core 3 linux installed on it. I would like to shutdown the PC (completely, switching off the ATX power supply) using the shutdown command from Fedora. When I shutdown the PC, the linux halted, but the PC does not switch off.
Just wrote to the display:

Power down.
acpi_power_off called

but nothing else happened.

Using MSI mainboard with the same installation procedure the shutdown works perfectly, the linux halt and the PC power supply switch off.
I think there can be some problem arround the acpi settings, but nothing can be set in the BIOS (the newest version) about acpi (just the ACPI Suspend Type - S1(POS), S3(STR) or S1&S3). And I can not set anything in Fedora about ACPI.

I hope I am understandable.
Can anyone help me to solve this problem?
Thanks in advance!
Elod