We're assuming that you're the one that's getting the Founder rank - the rank that holds the highest power out of all the ranks. Since nobody on the server has the Founder rank that can give the the rank in the first place, you're going to have to do it from the server's console or use rcon. We're not going to get in depth on how to access your server's console; if you're hosting the server yourself, you should be able to see the console anyway. Otherwise, go on a quick Google session and look up source rcon and HLSW. You'll be able to run server console commands from your own computer.
When you've joined the server and are ready to receive your rank, type in the command `serverguard_setowner `. This will find a player with the name that you've specified (in this case, specify your name), and give them the Founder rank. If everything goes well, you'll see a prompt in chat saying that your rank has been set to Founder.