I started playing pokemon Leaf Green and for some reason, whenever I save the game, when I reopen my Game Boy - the game starts all over again. Can anyone help me with that?
LeafGreen (and all other Generation III games) does not have save data tied to an internal battery. This means something else is wrong with the game, with possibilities ranging from user error to a fundamental problem. There are two plausible explanations, but only one is fixable.
Identifying fake Pokemon games can be difficult, but it's a good skill to have. I think this article is particularly helpful.
The game boy games (even the advance) have an internal battery that allows the game to stay saved even when it's off. But after a long time, the battery can die out, and when it does, you won't be able to save; this has likely happened to your game, so it can no longer save. Sorry about that. :(