Why won't my TV pick read my portable DVD player? (by 2 users)

I have a small TV/VCR combo (Daewoo) It has the yellow and white video and audio ports in the front. I tried to hook up a DVD player to it and it doesn't pick it up at all. I tried the DVD player on another small TV with the yellow and white inputs on the back and it works ok. This second TV also plays my karaoke CDs and the new one won't. Is something wrong with the inputs. I have never used these inputs and cannot find my manual. Thanks.