Ciao a tutti, .....mi dareste una mano ?

Ho un banalissimo form per tenere monitorata la pressione arteriosa che alla fine ha due semplici pulsanti
REGISTRA ----Che compila i campi correttamente
e
MODIFICA ---- Che dovrebbe reindirizzarmi su un'altra pagina (sempre all' interno della stessa cartella ) che dovrebbe darmi la possibilità di correggere i dati......MA INVECE , CLICCANDOCI SU NON SUCCEDE NULLA MI LASCIA SULLA STESSA PAGINA ,SENZA NEANCHE RESTITUIRE UN ERRORE

Come potrei fare ? .......

Grazie in anticipo!!!!!!

Ecco il codice

Codice PHP:
<form id="forminserisci" method="post" enctype="multipart/form-data" runat="server" action="<?php echo $_SERVER['PHP_SELF']; ?>" autocomplete="on">                     <table class="tableinserisci" align="center">                            <tr>                                <td align="center" colspan="8" class="registro"><h1 style="font-size: 60px;">REGISTRO PRESSIONE</h1></td>                            </tr>                                                      
 <tr class="lbl">                                  
<td class="lbl"; align="center">DATA</td>                                
<td class="lbl"; align="center">RILEVAZIONE</td>                                
<td class="lbl"; align="center">MAX</td>                                
<td class="lbl"; align="center">MIN</td>                                
<td class="lbl"; align="center">PULS</td>                                
<td class="lbl"; align="center">ORA</td>                                                                
<td class="lbl"; align="center">NOTE</td>                            

</tr>                            

<tr>                                
<td> <input type="text" id="data"  name="data" value="<?php echo date("d/m/Y");?>" size=" 14" autocomplete="on"></td>                               
<td><select id="rilev" name="rilev" value="">                                        
<option></option>                                        
<option>Fine</option>                                        
<option>Mattina</option>                                        
<option>Sera</option>                                    
</select>          
</td>                          
<td><input type="text" id="max"  name="max" value="" size="4" autocomplete="on"></td>                <td> <input type="text" id="min"  name="min" value="" size="4" autocomplete="on"></td>                <td> <input type="text" id="puls"  name="puls" value="" size="4" autocomplete="on"></td>                <td> <input type="text" id="ora"  name="ora" value="" size="4" autocomplete="on"></td>                 <td> <input type="text" id="note"  name="note" value="" size="0" autocomplete="on"></td>               </tr>                                                
 
<tr>                        
<td colspan="4"><input type="submit" name="registra" value="Registra"
style= width:" 161px; height: 55px; font-size: 25px; margin-top: 30px;</td>                        

<td><button onclick="location.href='Modifica'.php'" 
style="width: 161px;height: 55px; font-size:25px;margin-top: 30px;">Modifica</button>                        </td>                        
</tr>                    
</table>                
</form>