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/or
http://localhost/myfiles/index.phpYou can also replace the index.php file already in the C:\xampp\htdocs folder with your own index.php, then simply type
http://localhost/in your browser or
http://localhost/index.phpLet me know back what you see in your browser when you try the above instructions.