I have a similar problem, but mine has nothing to do with the keycodes. When I turn it on, everything works fine, and I can out my codes in. But when I select "Start game with selected codes" My screen just goes blue as if the system stopped working. I do the same thing for Ocarina of time and it works completely fine. Any ideas out there? My gameshark is v 3.0 and I have the collector's edition cartridge of Majora's Mask.
Which FireRed rom version are you using? Because V1.1 will not work in this game. We compiled a list of information with regards to cheat issues and solutions in this page here -gameshark-cheats-not-working/ and hopefully this will help you.
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