youtube videos no longer play on my iPad

For the past couple of weeks i've been able to view embeded youtube videos on my iPad. For whatever reason it doesn't work anymore. i touch play and nothing happens. The affects both presentations where it worked before and no longer does as well as new. please help. thanks
here's one of my prezi's. the videos work online but not on the iPad

http://prezi.com/3zz_3rzb02sn/?utm_ca...