Ensure that your URL setting in config is the actual server, not the redirect.

Unless your router preserves the hostname field, you won't be able to get this or many other scripts to work.  What kind of router are you using?

In forwarding requests to your webserver, it must not rewrite the http request.  Hmm, why don't we have you put the debug file in your hcl directory, and you can PM me the exact URL to get to it.  The debug file is attached below

hi, I have put the debug.php under the hcl dir.

when I open the hot page from my local machine, it works fine since I set the myhostname.com to localhost in the HOSTS file. But if the hot page is opened from other machines, it doesn't work right since myhostname.com is redirected by third party server to my ip address. Actually, even I put my ip address into the web browser, it still doesn't work right.

the config.php setting is set to myhostname.com for url though.

Ok, I get a 404 page error for the hcl directory and for the debug file.  You need to get your server/router issue taken care of before hcl will ever work.  There are resources on the web for setting up a server on a DSL/Cable modem. 

One thing here, many ISPs (particularly cable and dsl) are starting to filter incoming web requests, so you might want to start looking for some shared hosting for your site.  If anyone turns you in for running a commercial service on comcast, they will shut off your access (unless you have a business account, and even then they often will not allow you to run servers on the network).  Just something to keep in mind.