Why can't I change my desktop background?
Windows 7 Starter edition comes with one desktop background, which can't be changed or customized.
You can use Windows Anytime Upgrade to upgrade to another edition of Windows 7 that will allow you to change your desktop background (and get more features and functionality). For more information, see Upgrade to another edition of Windows 7 by using Windows Anytime Upgrade and Windows Anytime Upgrade: frequently asked questions.
If your desktop background has been replaced with a message that says Windows isn't genuine, you'll need to validate your copy of Windows before you can restore the original desktop background. Go to the genuine Windows website for more information.
Click the Start
and then click Control Panel
In the search box, type display, and then click Display.
In the left pane, click Change color scheme.
In the Color scheme list, click Windows Classic, and then click Apply.
In the Color scheme list, click Windows 7 Basic, and then click OK.