the problem is (most likely) in your S video - RCA conversion cable.
Svideo carries two signals, colour and luminessance, one should be filtered from the other when transformed into composite, a cheap adapter will have cheap parts and not work properly.
Also, because the colour is encoded, it is encoded to a standard, you may find that you need to change the video settings between NTSC and Pal... (try hooking an NTSC only video to a PAL only TV, I have the same problem with my old (american) SNES and my new (PAL only ) TV...
Some devices are just not compatable though!
(I've seen this with an ATI card and an epson projector)
if it's a decent TV I'd assume that it has an S-video socket, and an RCA socket, I'd suggest either buying an S-video lead to connect your computer to TV,
if you have a RCA socket on the computer then use the RCA sockets on the TV...
and forget about the converter!