Background can't be changed

Only recently i discovered that my laptop background had reverted back to the default 'Aurora' wallpaper. I can access System Preferences, but when I click on any of the background images, nothing happens. The wallpaper remains the same. This includes both my personal images and other default ones stored on the laptop.
The screensaver works fine as well, and i have not installed any new software or done any tweaking to my macbook.
My laptop is a Mac OS X 10.5.6.

Make sure you're logged on to the correct account. Setting wallpaper on one account and then logging on to another is one way the default Aurora desktop would show up again.

Regards.