What do you mean locked?
Do you know the ip of the router?
Have you tried to log onto the Router?
If you don't know the password for the router then yes, I suppose it is locked for you.
You seem to be indicating that you used to be able to connect on that telephone line using a specific login and password from one ISP.
Is this correct?
If yes, then, I can safely assume that you want to connect using a different login and password from another ISP.
I have to ask if the ADSL line you are using actually works. i.e. Does it Sync with the DSLAM?
It does and my first assumption was correct:
The login and password you are trying to use, is there a chance that perhaps the holder of the account has bound that account to their telephone port, which means that it will never work on any other telephone line?