Ipod nano help please

ok i need help with my ipod nano...i have been having mines for almost a year and in my videos section some of the videos are grayish or just totaly gray....but they dont play gray they just look gray before you play them so do any one know what i can do or where i should go to because i like thing too look like they should and ack like they should so do any one have any advice please help.........imani