Wake-on-lan only works so many times

Solution 1:

Chances are you are sending to an ip address which is not the broadcast address for the local network. What happens is that when you turn your machine off it loses the ip address but your switch/hub and other machines will keep this information in it's arp cache. When this cache expires you will not be able to WoL unless you use the broadcast address.

Solution 2:

Some things you could try :

1. Assign the computer a static IP address
2. Check if a BIOS update is available (take care!)
3. Update manually router's ARP table if you can telnet to it using arpadd. See :
   SpeedTouch Configuration: Wake up on LAN.