Who can solve this one?!

Ok I have a 4 inch colour LCD screen which I’m mounting on my PC. I have plugged it in but I can’t get a picture on it except for when the pc boots up. When it get to windows it goes blank. It has 2 composite connectors 1 red and 1 white. 1 of these is for the mono speaker and the other for video. I have plugged the connectors into the S Video cable that came with my GPU and it works only at boot. I have tried to change the resolution to 640 x 480 but I still can’t get a display. The LCD is a PCM-4NP

Where am I going wrong here?

My GPU is the X800XT PE 256MB AGP

Thanks for any help guys.

Have you set it up as two screens?

How do i do that?