WordPress form submit trouble

I’m writing a site with shop and chat.
I’m trying to admin users messages in a page.
In the header’s the submit function:

function ins_dom(){
    global $wpdb;
    $risp = $_POST['risp'];
    $i = $_POST['ins_dom'];
    $id = $id[$i];  
//must have comment
    if(!$risp){
        exit;
    }
// query
$wpdb->insert( 
    'm_comm', 
    array( 
        'comm_usr_id' => 1, 
        'comm_utente' => $id,
        'testo' => $risp,
        'risp'=>1
    ), 
    array( 
        '%d' ,      
        '%d' ,
        '%s',
        '%s'
    ) 
 ); 
return true;
};

And here’s the body:

<form Name ="ins_dom" Method ="POST" ACTION = "">
<table><tr><td>
id</td><td>
question</td><td>
answer</td><td>
submit</td></tr>

<?
    $dom=chiedi_2();
        if(count($dom)>0) {
            for ($i = 0; $i < count($dom); $i++) {
                $id[$i]= $dom[$i]->comm_usr_id;
                $testo[$i]= $dom[$i]->testo;
                echo "<tr id=$i><td>".$id[$i]."</td>.
                "<td>".$testo[$i]."</td><td>".              
                "<textarea  value='risp' name='risp' maxlength='200' cols='30' rows='4'></textarea></td><td>".
                "<INPUT TYPE = 'Submit' Name = 'invia' VALUE = '$i'></td></button></td></tr>";
            }
        };
        echo "</form></table>";
?>

Browser doesn’t notice errors I’m blocked here.
All I would like to do is to insert the query.
The form works pretty good and when I click the botton page refreshes but nothing appens