Every time that's happened to me it turns out to be a bad switch box. You can pick up an adapter from Atari age for 3 bucks. If its not that, it could be that your cord has gone bad. Going deeper, you might have cold or cracked solder joints on the mother board. Something could be stuck in your cartridge slot. it could be any of those. Or the board was compromised by whatever is burnt, I'd have to see a pic of it. If you're in the Fresno California area I can fix it up for you at Red Shell Repair.