HDMI monitor stops working when lap top lid is closed
From: Closing lid problem:
To make Ubuntu do nothing when laptop lid is closed:
Open the /etc/systemd/logind.conf file in a text editor as root, for example
sudo -H gedit /etc/systemd/logind.conf
Add a line HandleLidSwitch=ignore
Restart the systemd daemon with this command:
sudo service systemd-logind restart
If that didn't work set the following
IgnoreLid=true in /etc/UPower/UPower.conf