Have trouble invoking Apex in S-Control, even simple Apex won't work

Even very simple code won't work, nothing gets invoked. Please help. Thank you!

Apex:
lobal class myHelloWorld {

// eyCDUkymDHyd9MisHBFLPIYJm

webService static String getHelloWorld() {
String hello = 'Hello World';

return hello;
}

}

S-Control:

<script type="text/javascript" src="/js/functions.js"></script>
<script src="/soap/ajax/15.0/connection.js" type="text/javascript"></script>
<script src="/soap/ajax/15.0/apex.js" type="text/javascript"></script>
<script>
function getHello() {
var shello = sforce.apex.execute('myHelloWorld','getHelloWorld',());
alert(shello);
}
</script>

Test Page.