If you mix up the bottom left screw on the LCD connector plate you can scratch off the board under there which will cause this to happen. It's crucial that you don't mix up those screws, and if you do just don't put in the bottom left one just to be safe.
Try this: 1. Go to your home screen then press the menu button 2. You should see system settings on the list, click it 3. It should take you to your settings environment 4. Return to your home screen and click the app drawer icon ( the icon than takes you to where all your apps are listed) 5. Locate settings and drag it to wherever you want its icon to be. 6. If settings isn't listed in the app drawer then backup necessary stuff on your phone and restore to factory state.