Sony dvd player Model DVPNS78H

Sounds like the TV you are using does not support NTSC, the US TV standard. Try connecting the DVD player to some other TVs - something not more than a few years old would be a good bet, and a large screen plasma/LCD ideal as most of these are "multi-system" and handle PAL and NTSC automatically.
If the problem was the region coding you would be getting a message on the screen, something like "Cannot play due to area limitations".