Admin_menu function not working

So I’m trying to develop a custom plugin for a site that I’m working on, and I’m having an unexpectedly difficult time with it. Right now, I can’t seem to get a top-level menu to show up using the admin_menu function. I’ve been going around and around, and I can’t seem to figure out why. Does anyone have any clue what I’m doing wrong?

Here’s my code so far, with some details changed:

(also some database stuff above, but that seems to be in working order)

function myprefix_add_new() { ?>
	<div class="wrap">
          <h2>My Title Goes Here</h2>
        </div>
    </div>
<?php }

function myprefix_admin_menu_add() {
	$mymainpage = add_menu_page("My Page Title","My Page Title",1,__FILE__,'myprefix_add_new');
}

add_action('admin-menu','myprefix_admin_menu_add');

?>

Does anyone see what I could be doing wrong? Or have done wrong?