Did you ever find that when you work with external monitor and you close the laptop lid, the monitor become off?
The laptop is change to sleep mode not completely off, still this is annoying. The reason you want to close the lid is because you want to focus on the bigger screen and not having 2 display with the same content.
To fix this situation you need to open power options setting from control panel. The option when you close the lid are: Do nothing, Sleep, Hibernate, and shutdown.
You must change the setting to Do nothing for On Battery and Plugged in settings, click the Save Changes button.
Open Control Panel>Power Options>Choose What closing the lid does
Or you can search power options and press Enter
Make sure when I close the lid setting are set to Do nothing on Battery and Plugged in option.
Hope this short posting will help you fix the problem.