[SOLVED] checkbox frustration

[aebstract]

      if (!isset($_POST['checktos'])) {
$problem = TRUE;
$error .= 'You must agree to the Terms of Service to complete your order. <br />';
      }

 

<p align=right><input type=\"submit\" name=\"submit\" class=\"textfield\" value=\"Checkout\" /></p>

 

 

I just want to check if the box is checked, I've gone through about 10 different ideas and nothing is displaying the error when it isn't checked. I'm completely confused.