Aaika on "Form and action to a page"

Hello, i'm writing a simple plugin. I want to display on a page (by shortcode) a form, but when i submit the form, the browser returns me error 500.
Instead if i put action="" on self and a if(issset($_POST['submit'])) it works.
This is the form:

<form method="post" action="<?php echo plugins_url( 'check.php', __FILE__ ); ?>" id="info">
<table cellspacing="0" cellpadding="0" class="scheda_input" >
<tr>
<td colspan="4 ><h3>Dati Personaggio</h3></td>
</tr>
<tr class="aa">
	<td>Nome: </td>
	<td><input type="text" name="nomepg"></td>
	<td>Cognome: </td>
	<td><input type="text" name="cognome"></td>
</tr>
</table>
</form>

the file check.php do nothing: it display a simple Hello World.