Blinking line in s-video

I hooked up the cable as per instructions, its hooked to my tv via rgb (red yellow white) cables, although i've also tried it with the scart adapter on and the problem remained.

After hooking up the cables, I right clicked on desktop ->properties->settings-> then extended my desktop onto the second display (tv)

I have the resolution of it set at 1024 x 768 and teh refresh rate is 60hz, i've tried it at 70 and 75hz too...

btw, sometimes the the line moves up or down, sometimes its thick and dark, others its thin and light. it also moves at different speeds. this is random and different settings dont effect the speed etc of the line...

I have just bought an s-video cable and hooked it up fine, I et sound and picture displays fine. All apart from I get a blinking line moving up the screen, it goes off the top of the tv and back to the bottom, and moves up again, non stop...

I have an ati radeon x300 se 128mb hypermemory graphics card, if that is any use.

Thanks in advance.