If you can telnet or console into the router, you will want to verify that the "ip http server"/"ip http secure-server" or "http server"/"http secure-server" (depending on the firmware) are in the configuration. You will also want to verify that a username and password have been configured with the following syntax:
router(config)#user <username> password <password>
If you want you can post your configuration to this thread for us to look at. Please remember to remove any sensitive information.
Let us know if you have any questions.