If you are getting a message in every server that boots you out saying your account is in use elsewhere you simply must go to where you installed Steam. Be sure you remember your account password as it will require you to type all that in even if you have remember password checked.
In the steam directory just delete the ClientRegistry.blob. This a temporary file used by Steam for a few things and it seems some bad data must be in it if you get the aforementioned message.
(Solution was found by Driv3n)