Why isn't my s-video connection working?

I bought a brand new s-video cord for my television and computer, both of which have the right connection slots. I hooked it up and turned them both. I skimmed through all of my tv input channels and messed around with the setting while at the same time I was using all the function (Fn) combinations that I had looked up. I have a Dell-All-in-One so the combination should be Fn+F8 I think. I also have Windows Vistas if that helps. I even went into the display settings and followed different tutorials I looked up. Please help me, both are compatibile i'm just very technologically illiterate.