Why Cant I Double Click On My Desk Top Icons?

Im working on a windows vista computer. yesterday i tried opening a program through my desktop but it would not go. it will not even highlight. i also right clicked and nothing. from the start menu they work but then what would be the point of a desktop right? well i have also ran a virus and spyware program. i have defragged it and ran the registry cleaner. everything looks fine. any suggestions?