iMessage problem?

I couldn't send any messages with iMessage, so I turned it off and on again. Then, I couldn't log back into my iMessage. When I tried to log in, it just quickly switched back into the log in screen. When I logged in and it said "Verifying" it would switch back to the log in screen and I can't log in. Then, when I DO get it to work, it would say "Log in already taken" So, any help please?