the s-video in jack on your tv also might correspond with a different channel for display to work correctly than the normal video-in your dvd player/vcr works on.
I have an RCA tv which has a dvd player, vcr, and a jack for s-video. the dvd player connects via channel 92, the vcr connects via channel 91, and the s-video jack connects to the tv via channel 90.
it could be that you have all the settings correct, but that you're on the wrong channel. read in your tv's manual for the correct settings/configuration for hooking up s-video.
also, when your laptop display turns off, it's transferring the output through an output medium, which may be the vga-out or s-video-out. check your computer's manual for help on those settings.
~Branson