My desktop image & icons have suddenly disappeared?

My macbook was working fine yesterday and I shut it down last night. Today, when I switched on the power, I first noticed that my usual screen picture wasn't displaying (I just had a blue screen instead). I went to my system preferences and selected a new desktop image, but nothing changed - still just the blue screen. I then noticed there were none of the usual file and folder icons displaying on the screen, but looking at the desktop via Finder all the usual files etc were still there. I then tried dragging a file to the desktop from another location, but the file didn't copy like it normally would. Also my hotspots which are set up via Expose have stopped working (but the options are still set up in Expose through System Prefs).

This is all I have noticed so far, but can anyone shed any light on what has happened here and how I can put it right?

Thanks