Creating my personal theme: the theme doesn't show up in available themes

I don’t know much about wordpress themes but I do know HTML, CSS, and PHP to the extent that I can create a customized appearance for my website.
I created a folder and gave it the name that I wanted to be the name of the theme. Then I created all the required files: page.php, header.php, footer.php, sidebar.php, functions.php, 404.php, style.css.
I copied the folder into the themes directory of my wordpress install but the theme isn’t appearing in the available themes there.
I think I need to add something so that wordpress knows that it is a theme. But I don’t know what?
Please help..