RCA TruFlat 27F520T

I received a brand new RCA TruFlat TV from some friends that won it as a door prize.  They already had too many tv's so they gave it to me.  Everything works great on it except when I tried to hook up my DVD player.  I get audio, but no video.  The problem is not the dvd player itself because it works on a different set.  If there some special hook up or switch that I am unaware of?  For a brand new tv I don't think there should be this type of problem.  I would appreciate any heop.  Thanks....