Try not entering a username and type the enable secret in for the password. It might be configured to ask for the enable secret instead of local authentication. Default enable secret is "Cisco" (note the capital C).
Once telnetted in, you can check to make sure that HTTP(S) is active by looking for the commands:
(no) ip http server
(no) ip http secure-server
These commands would be toward the end of the configuration. You can disable/enable them by typing them into the config line without the "no".