The most obvious answer is that you have a wrong username/password combination. You would typically get another chance, which you have not indicated.<br>
TCP wrappers or inetd.sec would prevent you from ever seeing a login prompt in the first place.<br>
Another possibility is that you successfully authenticate yourself, but due to a profile problem the system is unable to spawn your shell. This might be indicated by seeing additional messages from the system following the password entry, indicating an attempt (albeit unsuccessful) to initialize your environment.