motherboard does not turn off

I have to install a video capture card on an Asus M2Avm motherboard:
I can use a pci-express card or a pci card (each card has four conexant and
a pci-bridge).
Both the card work well, but when I use the pci one, if I click on windows'
turn off button,
The operating system turn off, but the machine remain on ( Processor and cpu
fan continue to run).

Can any one help me to resolve this problem?


Regards,

Gianluca