Problem selecting items on the Desktop

This is embarrassing, but I can't select my icons on the desktop anymore. When I try to double-click on a file or folder, my Mac makes the "not allowed" noise and doesn't open the file. It's almost like when you have a dialogue box open, and you need to make a selection before the computer will let you do anything else.

I'm using Leopard, and I just turned on Spaces--does that have anything to do with it? In Spaces, can you access what's on the desktop from any Space?

Thanks!

 

Actually, it seems like a problem with my Finder, which doesn't work at all. Is it possible to restart the Finder, or do I have to restart the whole computer?