APEX

Hi.. When i set an onLoad attribute to page, window.open method does not work but when i set it to onClick it works..

For ex:
****************************************************************************
-----HTML Header----
<script>
function kapat() {
window.open('http://yahoo.com'); ------->does not work
alert('z'); ------->works
}
</script>

------Page HTML Body Attribute------
onLoad="kapat();" ------->onLoad event


****************************************************************************

-----HTML Header----
<script>
function kapat() {
window.open('http://yahoo.com'); ------->works
alert('z'); ------->works
}
</script>

------Page HTML Body Attribute------
onClick="kapat();" ------->onClick event



Any body knows why??