Source: Nintendo.com
customer service section
[quote]
NES Game Pak Troubleshooting
Note: It is possible that the problem you have may be game play related. For example, if you cannot defeat a particular enemy, or are missing an item you need to complete an area, the problem is likely game play-related and there is nothing wrong with your game. Please check our game play help for assistance. Otherwise, follow these troubleshooting steps:
1. Insert the Game Pak into the system. The Game Pak label should be facing up as you slide it in (original NES) or towards the front of the system (New-Style NES).
2. Make sure the Game Pak firmly clicks down into place.
3. Remove all accessories to see if the Game Pak works correctly without the accessory. If the game does work correctly once the accessory is removed, then the game pak and the accessory may not be compatible. Check the game pak instruction manual.
4. Do not blow into your Game Paks or systems. The moisture in your breath can corrode and contaminate the pin connectors.
5. Cleaning the Game Pak with a Cleaning Wand may help remove any debris or contamination from your Game Paks.
Due to the age of the system, we no longer offer factory repairs directly from Nintendo. Please click here to find out what options are available for repair or replacement of your product.
[/quote]
You won't listen to me, how about Nintendo?