Everytime i try to change my desktop backround when i go into desktop and screensaver in system Preferences it doesn't respond and i can't change it.

Close all windows and quit all applications.

Hold the option key down and click the "Go" menu in the Finder menubar.

Select "Library" from the dropdown, then "Preferences" folder.

Look for these three files.

com.apple.screensaver.plist

com.apple.desktop.plist

com.apple.systempreferences.plist

Right click each one of those and select " Move To Trash" from the contextual menu.

Restart the computer.