Make sure your PC Network Interface stack is properly configured to accept a WOL. For example on my win 7 system using a Realtek interface on the Mobo, I need to go to the network device properties select 'Configure' and go to 'Advanced'. Scroll down the list and set 'Wake On Magic Packet' to enabled. Other network interface's may be slightly different but they all generally have some method for enabling and disabling WOL