If you encounter these kinds of problems, we suggest cleaning the bronze prongs at the base of the cartridge and on the inside of the DS itself. Dirt or grime that accumulates on these prongs can prevent the game from being read. This is most easily done at home with a q-tip dipped in rubbing alcohol. Allow the game and system to dry fully before attempt to insert the game.
If cleaning the game doesn't work, please read this article regarding our warranty policy.