Well without more code it’s hard to tell but one thing is you are wrapping a shortcode with php tags. My guess is you have error logs turned off or you’d see Santax error unexpected '[' on line XXX
If you are using the post/page editor you want to use[contact-form-7 id="181" title="Contact form 1"] (see no php tags)
If you really want to use php tags (or embed the form into a template) you could do something like
<?php echo do_shortcode( '[contact-form-7 id="181" title="Contact form 1"]' ); ?>
If that doesn’t help please post more code.