When my son's HeartGold DS game is loaded into his DSlite or his sister's DSLite the screen goes black shortly after starting. You can hear the music but can't see anything. It doesn't happen with any other game. The game is several moths old and has not acted up at all until now. What can we do?
How well does your son handle the game? I can't really make a clear guess without knowing more. You can't purchase a new one and swap his data, so I haven't a good answer for you at the moment...sorry!
If it happens with multiple DS's, it's a good possibility that the game card has dust, fingerprints, or dirt on it. Try cleaning it with a Q-tip and rubbing alcohol. Be sure to let it dry afterwards and don't use too much alcohol.