lake Hooking up PC to TV with S Video?

I am trying to watch whatever is on my PC on my TV. I have all of the necessary cables but I just don't know how to change the settings on my PC to get the visual on my television. I have an ATI radeon graphics card, and Windows Vista 64 bit. I connected the s-video cable from the back of my PC to an RF modulator, since my older tv does not have an s-video jack actually right on the tv. then from the rf modulator I ran a coax screw in cable from it into the spot on the back of my tv. Still no video! can someone explain how to make this work?there