If you've already created the dns a record that points www.abc.com to the ip address of your server, then you still ned to add that host name in the IIS bindings for the IIS web site. The bindings are where the ip address is assigned for the web site in IIS. Look in IIS in the configuration for the web site you should see bindings. You need to add a binding with the host name www.abc.com
Hope that helps,
Joe