I can't seem to be able to get the National Dex in Pokemon Platinum! Help me plz!!!?

I have seen all 210 Pokemon in the Sinnoh Dex but Professer Rowan won't look at my Poke Dex. I got a cheat online that unlocked the National Dex before I got all 210 Pokemon so maybe that may be the reason. I don't know. I beat the Elite Four and went on the ship from Snowpoint City and went to the Fight Area and everything but I can't seem to be able to get the National Dex. Anybody got any ideas???|||probley you miss something in your game or probley the cheat mess up the game|||you have to restart your game :( sometimes cheats can really screw your game up...|||look in http://pkmn.net/?action=content%26amp;page=vie鈥?/a>