Cannot play TV programmes-Help please

[stocksie81]

Hi I recently bought a 7" tablet for my toddler. I hve saved episodes of her fave programmes into an SD card but can't get them to play. They are showing as there with the front cover of the show but when u press play the timer is counting down to show it is playing but the screen doesn't change and there is no sound. Any advise greatly appreciated as I'm totally clueless!!