The security chip can have just as big an effect as the pin connector. I got my console back to about 100% start-up by replacing the connector and disconnecting the chip.
Get your games clean with alcohol and a q-tip, and never put a dirty game into the system.
NEVER EVER blow on the cartridges either, it just causes corrosion from your spit. The reason it makes the games work sometimes is mostly because you've taken the game out and reseated in the pin connector. If you think it's dusty, get a q-tip.