Make sure in your firewall that all the ports that XAMPP uses are allowed through.
xampp-portcheck.exe will give you the ports and make sure they are only occupied by the XAMPP components that are running - if you try this portcheck with the Apache and MySql stopped then they should all show free.
What do you see if you go to http://localhost:8080/xampp/index.php
after you changed the Listen directive.
If you can I would revert your httpd.conf file back to the defaults that you had when you installed XAMPP then we can dispense with the 8080 bit and then, after we get it up and running, you can change the Listen directive if you need to, it makes it easier to troubleshoot.