My pc don't stop

Hello,
I have installed debian testing (but with unstable it is the same) on my computer. THe mainboard is a DFI 915P-TAG. My problem is that when I want to stop the PC, the system shutdown, and I have the message : "ACPI_POWER_OFF" but the pc don't stop completly. I have installed the acpid package and I have the 2.6.12-1-686 kernel.
Is there an issue ?

thanks :)

--
yves piel

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