When creating an account, I get the message:
A Steam account already exists with that contact email address. If you have previously created a Steam account, you should use the existing account rather than creating a new one.
This message will only display if your email address is already associated with an existing Steam account.
Creating a new Steam account will not allow you to register games which have already been registered.
Once you have created a Steam account and registered your CD Key or purchased a game on Steam, that game is permanently tied to that particular account. You can not transfer the game to a different account once you have registered it.
If you are attempting to access games that belong to an existing Steam account, please visit the Steam Help site for assistance reclaiming your prior account.