Need to make sure you understood me:
- right click on your desktop and select "Display Settings"
- The default window that opens should show any/all displays that are currently available
- You can click "Identify" to correlate which number on the diagram corresponds to which monitor
- Click/select the diagram monitor that corresponds to your laptop screen (this should give it a colored infill compared to the other(s))
- Scroll down to "multiple displays" and in the drop-down box, select "disconnect this display"
- Your laptop screen will no longer be used (if you open the lid, the screen will be blank). Your mouse will not travel to it either.
The above setting will apply only for the setup that is currently active. ie, if you disconnect your external monitor(s), the laptop screen will re-activate.