First make sure the s-video cable is plugged in from pc to tv, then reboot computer... then follow steps below.
Its possible that maybe you have the video output in PAL or SECAM, set it to NTSC 3.58 and reboot the computer with the s-video cable plugged in. Unless you're in Europe, then set it to PAL, but Europe uses those Scart ports... and S-video I think. My TV is an international model, multi system JVC w/ s-video... no scart.