Four things are required for transparent icon backgrounds:
1) start > Control Panel > System > Advanced > Performance Settings > VisualEffects - check
"use drop shadows for icon labels".
2) Right-click on Desktop -> Arrange Icons by > Lock Web items must be cleared.
3) If you have any web content on your desktop, transparency won't work.
To check for web content: start > Control Panel > Display >
Desktop > Customize Desktop > Web - make sure all checkboxes are clear.
4) Wallpaper must be an image file, not html.
(c/p)