Normally, modal forms will appear when the user clicks a button. In some cases, you may want the form to appear as the page loads, with no action from the user.
If you are actually trying to restrict access to the page you should use a page lock gate, which is available on most accounts.
This article will show you a small trick to make a modal form appear on page load.
First of all you need a page with a gate already embedded.
Take the modal embed code and add it to the end of the URL.
Make sure it is placed after the query string parameters (represented by: ?) and remove any other bookmarks that may already be in the URL (represented by: #).
You can now distribute this URL through your site architecture, marketing campaigns etc.
If you are still having issues, fear not, GatedContent.com is on hand, simply click "+ New Support Ticket" above.