I registered 6 files in minecraft. None of them are available to log into. I even wrote them down but it still won't work. And I have to play offline and multiplayer won't work on offline.
Well, judging by the fact that you said "TNT", I assume you mean you want to play on "retail" servers as opposed to "classic" servers.
In order to do this, you need to buy the game. To buy the game, you need to log into the account you created and then press "Buy Game" on Minecraft.net. Simply creating an account, which I assume is what you were doing, only works on "Classic" servers.
If you did actually buy 6 Minecraft accounts, I suggest contacting Mojang Support.
Can you also not login to http://www.minecraft.net/login?
If you happen to have bought Minecraft around Jan 19, there seems to have been an issue with Mojang's system:
Maybe you should also send them an email, email@example.com