I can't play on new or existing worlds but I can join friend's world and play

When I start Minecraft PE, if I try to create a new world, or try to continue with a saved world Minecraft closes itself down. The icons of the saved worlds are now in grayscale not colour. However I can still play minecraft if I join a friend's world.
It has been like this for the last 3 updates. I have tried un-installing and re-installing but it has no effect on the way the program works.