It is probably because you are actually putting an incorrect username or a password. Check your password again and make sure the caps lock key is not turned on, on your keyboard. In case it still does not work, you might have changed it to something else and might have forgotten the new password. If that's not the case, then somebody must have hacked into your account and must have changed the password. In this case, you can request for a change of password by clicking on the 'Forgot Password' section on AOL. The section will ask for a secret question and answer that you might have entered when you had registered your account with AOL. If you enter the right details, your password will be reset and you will receive a new password immediately right there or in your secondary email account that you might have entered when you would have registered.