Game crashing at loading screen of starting world.

The world is several years old, it's been up since the 360. The main issue is that I went to the nether, then tried to come back to the overworld. Afterwards, the game froze at the loading screen, trying to generate the world, then crashed. I re-launched the game and tried to load the world afterwards, but every time I try, it seems to go ahead and freeze at the loading screen then crashes again. I have no idea what to do and I don't wanna lose this world.. I've spent so long on my world..