How do I prevent my laptop from going to sleep when I close the lid while using an external monitor?
Open the Control Panel and go to Power Options, then select 'Choose what closing the lid does.' Set the action to 'Do nothing' and click OK. Under the 'Plugged in' section, also select 'Do nothing' and save the changes. (Page 7)
From the official HP Laserjet Pro Mfp M426fdw manual, page 7
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