you have not run query try to run with mysql_query()
try
$BIS = "SELECT COUNT(*) as count FROM Voti WHERE sito='$sito' AND utente='$utente'";
$topics= mysql_query($BIS);
while($row = mysql_fetch_array($topics)){
or try for count rows
$BIS = "SELECT * FROM Voti WHERE sito='$sito' AND utente='$utente'";
$topics= mysql_query($BIS);
$count = mysql_num_rows($topics);