Using conditional logic hides entire form

It's difficult to say since you didn't include a link to your form. One reason this happens is because of a raw, or noformat shortcode that's been added to the theme. If you look near the footer of the page, you'll see some inline script for the conditional logic. Check to see if the script is wrapped by a <p > tag. If so, that's probably the case.

You can refer back to this thread for more information.

http://forum.gravityhelp.com/topic/form-worked-for-a-while-and-then-disappeared#post-6394

The other reason could be that you've embedded the form in a widget or via the function call and haven't enqueued the scripts necessary for the conditional logic functionality.

When using a Gravity Form in a sidebar widget or embedding it anywhere using the function call, you need to manually enqueue the scripts and CSS by placing a short script block in your theme's functions.php file.

wp_enqueue_script("gforms_ui_datepicker", WP_PLUGIN_URL . "/gravityforms/js/jquery-ui/ui.datepicker.js", array("jquery"), "1.3.9", true);

wp_enqueue_script("gforms_datepicker", WP_PLUGIN_URL . "/gravityforms/js/datepicker.js", array("gforms_ui_datepicker"), "1.3.9", true);

wp_enqueue_script("gforms_conditional_logic_lib", WP_PLUGIN_URL . "/gravityforms/js/conditional_logic.js", array("gforms_ui_datepicker"), "1.3.9", true);

wp_enqueue_style("gforms_css", WP_PLUGIN_URL . "/gravityforms/css/forms.css");

Without this, the conditional logic scripts, datepicker script, form CSS and other elements needed for the full form functionality aren't loaded.

You can find more information at the URL below

http://www.gravityhelp.com/documentation/embedding-a-form/