When I save my Pokemon Yellow the next time I turn it on it's all gone, please help.
The cartridge is corrupted. This happens to old GBA games. When a game is really old, it tends to stop working. I'd say you should return it to the store and play an emulator instead.
You can fix it, but it's a long and tedious process. You can get more information here. Good luck!
Your GameBoy game's battery might have run out, or your game got corrupted, that happens when you do not use it for a while. hope I helped :D(I dont think so)