Does the game usually says" the save file is okay" before the continue,options,New game appears?
If it does, Im sorry to say this, But your cartridge is fake.
Heres some tips to tell you if a pokemon cartridge is fake.
The cartridge itself is colored gray.
The game always says,"the save file is okay"
When your save file has been deleted, Its Fake
Note:
There are pokemon cartridges that looks like legit but its not,(some fake Pokemon Cartridges has a right color casing,)
You could make use of the tips i wrote above. =D
EDIT: I FORGOT TO SAY THIS,IF YOURE CARTRIDGE IS LEGIT,THEN MAYBE
THE CHIPS OR WHATEVER INSIDE THE CARTRIDGE MAY HAVE BEEN DAMAGED,
HAVE YOU ACCIDENTALLY SPILLED WATER ON IT?,DROPPED IT? SAT ON IT? OR ANYTHING LIKE THAT?