Connecting VCR/DVD combo

My 80 year old father has this model TV,(DS25390) and I bought him a Magnavox DVD/VCR combo and am having trouble hooking it up. I bought a modulator, hooking up the TV to the TV hookup in the back of the modulator, the cable cord (he has no cable box, just a cable that comes through the wall)to the antenna on the back of the modulator, the red/yellow/white cables hooked from the VCR/DVD to the back of the modulator (under VCR/DVD column) The player is running, but have no picture from the movie or no audio from the movie. Have the TV on channel 3, modulator is set on channel 3. What am I doing wrong. HELP
We have a Phillips VCR-DVD combo and a Cox communications cable box and a Samsung wall TV and we are having the same problem. We tried the modulator but the light went on red meaning it wasn't hooked up correctly. If it doesn't work is it just a matter of the TV not being on channel 3?