Cannot change desktop background in Windows 7 Home Premium

thank you

after deleting that file my desktop walls changes normally

http://www.withinwindows.com/2009/10/20/hp-and-stardock-team-up-to-ship-netbooks-with-custom-wallpaper-themes/ 

Try this:

1. Open the control panel and type "experience" into the search box. One of the options should be "Check the Windows Experience Index'. Click on that, and make sure your video score is higher than 3. If any are blank, you've never seen this screen before, or you've upgraded your video drivers since installing windows then click on Refresh Now and let it do its thing.
2. Now type "glass" into the search box at the top right corner of the control panel. Select "Change Windows Glass Colours" or "Enable or disable transparent glass on windows" - they both bring you to the same screen. Make sure that enable transparency is selected. This is also where you can pick eggplant or whatever.
3. Now right click on the task bar beside your icons, and pick properties. At the very bottom of the taskbar tab is a check box for aero peek. Turn it on if you want the previews for your windows when you move your curser over the icons. I believe this requires the newer style taskbar though, so if you've changed it to the old style it won't work.

If none of that is what your looking for, go back to the windows experience index page. On the left hand side there should be an option 'Adjust visual effects', this lets you manually choose animations. Aero Peek and transparency can also be activated from this menu.

Hope some of this helps!

Thank you, but mine is everything in "Check the window experience index" is above 4.0, transparency is enable in "glass" but I still can not change the desktop background. I can not even use other built-in themes of Microsoft.

Thank you, thank you, thank you.  I, too, went crazy wasting time and energy trying to fix my background.  I used Ty the IT Guy's solution and Bam - it worked easily and fantastically.  I am now at peace.  Thank you again!