Error posting form data to same page - php

Question

I have some info that is listed out. One of those fields is submit_date which has the date an application was submitted. On top of this list, I wanted to make a form where with drop down menus we could choose an initial date and a final date and then the list would only show applications submitted between that time range. I got the sql to work and made the form but for some reason whenever I click submit the entire list disappears.
<form name="yearRange" action="index.php" method="post">
Year1:
<select name="year1">
<option value="2010">2010</option>
<option value="2011">2011</option>
<option value="2012">2012</option>
<option value="2013">2013</option>
<option value="2014">2014</option>
</select>
Month1:
<select name="month1">
<option value="01">January</option>
<option value="02">February</option>
<option value="03">March</option>
<option value="04">April</option>
<option value="05">May</option>
<option value="06">June</option>
<option value="07">July</option>
<option value="08">August</option>
<option value="09">September</option>
<option value="10">October</option>
<option value="11">November</option>
<option value="12">December</option>
</select>
Day1:
<select name="day1">
<option value="01">1</option>
<option value="02">2</option>
<option value="03">3</option>
<option value="04">4</option>
<option value="05">5</option>
<option value="06">6</option>
<option value="07">7</option>
<option value="08">8</option>
<option value="09">9</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
<option value="13">13</option>
<option value="14">14</option>
<option value="15">15</option>
<option value="16">16</option>
<option value="17">17</option>
<option value="18">18</option>
<option value="19">19</option>
<option value="20">20</option>
<option value="21">21</option>
<option value="22">22</option>
<option value="23">23</option>
<option value="24">24</option>
<option value="25">25</option>
<option value="26">26</option>
<option value="27">27</option>
<option value="28">28</option>
<option value="29">29</option>
<option value="30">30</option>
<option value="31">31</option>
</select>
Year2:
<select name="year2">
<option value="2010">2010</option>
<option value="2011">2011</option>
<option value="2012">2012</option>
<option value="2013">2013</option>
<option value="2014">2014</option>
</select>
Month2:
<select name="month2">
<option value="01">January</option>
<option value="02">February</option>
<option value="03">March</option>
<option value="04">April</option>
<option value="05">May</option>
<option value="06">June</option>
<option value="07">July</option>
<option value="08">August</option>
<option value="09">September</option>
<option value="10">October</option>
<option value="11">November</option>
<option value="12">December</option>
</select>
Day2:
<select name="day2">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
<option value="7">7</option>
<option value="8">8</option>
<option value="9">9</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
<option value="13">13</option>
<option value="14">14</option>
<option value="15">15</option>
<option value="16">16</option>
<option value="17">17</option>
<option value="18">18</option>
<option value="19">19</option>
<option value="20">20</option>
<option value="21">21</option>
<option value="22">22</option>
<option value="23">23</option>
<option value="24">24</option>
<option value="25">25</option>
<option value="26">26</option>
<option value="27">27</option>
<option value="28">28</option>
<option value="29">29</option>
<option value="30">30</option>
<option value="31">31</option>
</select>
<input type="submit" name="submit" value="Submit" />
</form>
<?php
if ($DBConn->numRows() > 0) { ?>
<div align="center">
<table border="1" align="center">
<tr>
<td> </td>
<td> </td>
<td><strong>Name</strong></td>
<td><strong>Submit Date</strong></td>
</tr> <?php
$date1="";
$date2="";
if(isset($_POST['year1']) && isset($_POST['year2']) && isset($_POST['month1']) && isset($_POST['month2']) && isset($_POST['day1']) && isset($_POST['day2']))
{
$date1 = $_POST['year1']."-".$_POST['month1']."-".$_POST['day1'];
$date2 = $_POST['year2']."-".$_POST['month2']."-".$_POST['day2'];
}
else{
echo "error";
}
$query = "select * from table1 where submit_date > '$date1' AND submit_date < '$date2'";
$sortQuery = mysql_query($query);
while ($row1=mysql_fetch_assoc($sortQuery))
{
?>
<tr>
<td valign="top"><?php echo $row1['lname'] . ", " . $row1['fname'] . " " . $row1['mname']; ?></td>
<td valign="top"><?php echo date('Y-m-d', strtotime($row1['submit_date'])); ?></td>
<?php } ?>
</tr> <?php
?>
</table>
</div>
<?php
} ?>