ipad doesn't play mp4

Hi, I have this problem with ipad and movies ! i bougt a new ipad 4 ( had ipad 2 ) did everything like previous, made video convertation to mp4, putted that i can manualy manage videos, after all this i put on video in itunes on ipad and then it aperas in light gray ( not black like they should be) letters and does't show movies in ipad ! then i did everything the same with my iphone 5 everything went good and on iphone movies apear ! so i thought in ipad 4 i have to just press some button to aper them ! please help me ! i'm confused !