1. In the Finder, hold down the Option key and then click on "Go" in the menu bar.
2. Click on "Library".
3. In the Library, go to the Preferences folder.
4. Find the file called com.apple.systempreferences.plist and drag it to the Desktop.
5. Re-start your computer.
With luck, that will fix the problem. If not, go back to System Preferences, be sure the settings are what you want, and if they are not, change them.