Hi I am trying to start the designer through the URL "

Is this your first time logging into the environment?

See:
forum.appian.com/.../Starting_and_Stopping_Appian

Thanks for replying. I have seen that page and tried with the username and Password as it was mentioned on the page but no positive results.

What server and port are you defining in your custom.properties file?

conf.suite.SERVER_AND_PORT=localhost:8080

and JBOSS is on 8081

It is recommended to use your fully qualified domain name or IP address here. Additionally, this should be the location of your application server.

forum.appian.com/.../Required_Configurations

Also When I start appian by executing <APPIAN_HOME>\\server\\_scripts\\start-suite.bat it opens various windows but i am not able to see jbosssvc.exe process in task manager. Please suggest.

That script starts the Appian engines not the application server. Please see the product documentation for details on installation and start up

as well as JBOSS is also running is there is anything else need to start....

Anuj, if I understand correctly:

1. You can see the login page
2. Executing from a command prompt <APPIAN_HOME>/server/_scripts/diagnostic/checkengine.bat -s
reports all engines are in Okay status
3. The only issue is you can't login with the default credentials. Correct?

Is this a new install? Because every time you install Appian you can login with the default credentials only once, because you are asked to change the password for this account. Most likely what happened was that you or somebody logged in using the default credentials, he/she was asked to change the Administrator password, he did it and now nobody remembers the password.