- First, power off your MacBook Pro
- Then, when you power up, hold down the cmd+option+P+R keys all at the same time
- When you see it cycle round and you hear the startup sound again, let go and let your MacBook Pro boot up as normal.
This on its own may resolve the problem. The other method that runs in conjunction with this involves a little terminal:
- Open up Terminal on your MacBook Pro
- Type in cd ~/Library/Preferences/ then press enter
- Then type rm com.apple.desktop.plist and press enter
- Finally, type killall Dock and hit enter again
This command will delete the settings file listed in the second line, and restart your dock so you're not running with any faulty preferences anymore. It also seems to set your wallpaper back to the stock, Mountain Lion wallpaper, so that may be a good sign that you did everything right.
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