SP.UI.ModalDialog.showWaitScreenWithNoClose('Loading...', 'Please wait while the content loads.', 60, 270);
You can also customize using a wrapper class like this.
function LoadingScreen(title, message)
{
return SP.UI.ModalDialog.$1I_1(title, message, false, false, null, null, 270, '12px 12px 4px 6px', 0);
}
LoadingScreen('Title', Wait message.');
you can also try using $20() instead of $1I_1. Play with it and you will get the hang of it...
:) Thank you