Showing Layers

I made this script, always works but for some weird resion it just doesn`t work any more,
Does any one know why.

<script>

function layers( divID )
{
if (document.getElementById) { obj = document.getElementById(divID); }
else if (document.all) { obj = document.all[divID]; }
else if (document.layers) { obj = document.layers[divID]; }

return obj;
}

function show_layer ( divID )
{
var obj = layers ( divID );

obj.style.display == ''
}

show_layer ( 'test' );

</script>

<div id='test' style='display:none;'> this is a test layer </div>