Hi sounds like the common fault found with these old retro consoles. Flashing light is mostly because the system does not make good contact with the game. which may be because of a worn out connector pins in side the console or dirty games recommend cleaning all your games with a game cartridge paste cleaner and replacing the connector pin with a new one. see
http://www.gameoz.com.au/store/nintendo-entertainment-system/nes-accessories/ they carry these items and included photo instructions.
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