How to configure Apache to listen some different port?

I am facing problem in starting XAMPP. First of all it gives me error messages in RED when i start XAMPP control panel. When i click on START APACHE, it starts it but when i open localhost it gives me the following error message.

Not Found

HTTP Error 404. The requested resource is not found.

I have tried various ways to resolve this problem but it isn't solved yet. Kindly guide me.

Thanks.

checklist

• first run XAMPP installer by UAC(User Account Control) and Antivirus off and run it as admin
• uninstall previous XAMP installation
• turn off IIS temporarily (which will use default port 80)
• change the port to some free valid port by following below guide
  • summary (Locate the file httpd.conf. This file should be found in C:\xampp\apache\conf folder or via config button in XAMPP control panel and search for 80 port and change it to something like 1234

http://complete-concrete-concise.com/web-tools/how-to-change-the-apache-port-in-xampp