Existing world won’t load.

To whom is reading this,

Hi there! I have been experiencing problems with my existing worlds on Minecraft Version 1.2.10.
Whenever I load up a world I have created or downloaded. It says ‘Loading resource packs’ then ‘Saving world’. Then it goes back to the world menu.

I don’t know if it is just my Game messing up or if this is affecting anyone else. But I hope you can look into this bug.

Many thanks! P.S I hope you can fix this ASAP as I really wanna rejoin my friends