Most laptops have a key combination that uses the FN key in combination with one of the Function keys. You should see pictures on some of the function keys on your laptop and one of them should look like two screens (rounded square). You would hit FN and then that function key and it will switch between the usual options of Laptop screen only, Laptop screen and External Monitor (LCD in your case), and then just External screen only.
If you can't find this key combination, then please post the make and model of your laptop and I will see if I can't find that key combination for you.