Using A Div To Shade The Background?

What I want to do is a button that, when clicked, shades the screen and opens a new box above it. The box code works fine alone, but if I add the javascript that shades the screen, the button won't work at all.

I use a div as the button, with an onClick method that changes the box.display from none to block or the opposite.

This is the function that changes the display. If I take out the whole first part (the background part), it works fine (though at the first time I have to click twice to show the box)

function showBox ( method ) {

background = document.getElementbyId( 'shade' );
if ( background != null ) {
background = background.style;

[Code].....