Composite video from dvd versus from camera?

I've a weird problem with a new portable screen display. It's the Pyle View PLMN9SU. It's an interesting device with composite video input, SD/mmc card support, mini-USB input, AV input, and a rechargeable internal battery. I think it's designed to be display for DVD players and I bought it because it's advertised with 'AV input'. What I'd like to do is hook various cameras to the monitor via composite video and use it as a portable monitor. But no matter how I connect cameras to the monitor I get no video at all. Yet when I connect a DVD player or an old VCR using their composite video output it works fine. So my question is what's the difference from video output from a DVD player and video ouput from a composite video camera. I thought maybe my camera was too hi resolution and dropped back to an old res camera I still get no video.

Alternatively how can I get composite video converted to usb port input. I tried an rca to usb cable laying around and still nada.

Thanks for any ideas.