it has happened to me too.
The solution is simple. Start your machine in safe mode. To do this, shut down your machine, start it up and press and hold the "shift" key. Release it once you see the apple logo.
You will get a menu, choose to start osx in safe mode. Once you are in you will see that all your icons are restored and ok. Now you can restart and go back into normal osx mode and everything will be ok!
Hope i helped