To maintain transparent icon backgrounds with drop shadow on your desktop try the following simple steps to reset:
1) Wallpaper must be an image file, not html web page
2) Go to System Properties > Advanced > Performance Settings > VisualEffects and check "use drop shadows for icon labels". In Windows 8 search for "Adjust Appearance" and choose "Adjust for Best Appearance" or choose a custom setting where the last option, "Use drop shadows..." is checked.
3) Right-click on Desktop ->Arrange Icons by>Lock Web items must be cleared.
4) If you have any web content on your desktop, transparency won't work. To check for web content: Display Properties>Desktop>Customize Desktop>Web - make sure all checkboxes are clear.