Assuming you have a default XAMPP installation in C:\xampp, have you tried this:
Create a folder in C:\xampp\htdocs called myfiles and put your index.php file in this folder.
Now type in your browser:http://localhost/myfiles/
You can also replace the index.php file already in the C:\xampp\htdocs folder with your own index.php, then simply typehttp://localhost/
in your browser orhttp://localhost/index.php
Let me know back what you see in your browser when you try the above instructions.