So you're broadcasting a magic packet with the LAN adapter's MAC but the adapter is ignoring it?
Are you sure the power supply has the power available to bring up the system when it's off?
You need 1A minimum available on the +5VSB lead. Check for a label on the side of the power supply, showing outputs.
And it needs to be in 'soft off' mode... the green LED down by the USB headers at the 'bottom' of the board (if it's standing on the edge where the CPU is near the top) needs to be lit... if that's off, WOL won't work.
And yes, there should be an option in the BIOS to enable it too. If you're using the gigabit LAN adapter on the PCI express bus, the option should be called 'Power on by PCIE devices'.