Window.open And Settimeout

I would like to use setTimeout and window.open methods to pop up
window every 5 minutes. I can only manage to make the window to pop up
only twice.

function openWindow() {
window.open("popupwindow.htm", "OpenedWindow",
"width=320,height=240, scrollbars=yes,resizable=yes,status=yes");

}
function settime() {
setTimeout("openWindow()", 300 * 1000);
}

So what is the problem that is making the window never to come back
when the user closes the popped window the second time?