Checkbox

<script type="text/javascript">
function checkTheBox() {
var check = document.getElementById('a').checked;
var but = document.getElementById('b');

check ? but.disabled = false : but.disabled = true;
}
</script>

<input type="checkbox" id="a" name="checkbox" value="blub" onclick="checkTheBox();"> blub
<input type="submit" id="b" name="submit" value="los" disabled>