Strange error with the Loop

Hello.
What is wrong with this loop? I got syntax error and can’t figure out what is wrong.

here is my source code:

<?php if(have_posts()) : while(have_posts()) : the_post(); ?>

This make an error at the bottom of the file.

If I comment out like this, the syntax error get away.

<?php if(have_posts()) // : while(have_posts()) : the_post(); ?>

or if I replace : with ; the error also go away. But that is not correct use of the loop and display of course nothing.

I am using Dreamweaver CC on Window 8.1