I own a Lenovo Thinkpad E540 made in 2014. It runs Ubuntu 20.04
A few days back, the laptop refuses to go to sleep when I close the lid. But goes to sleep if I give
 $ systemctl suspend
In the Energy settings I can't see the lid button specified any more.
How could I tell if it is a software problem (switch not detected) or a hardware problem (switch dead) ?
And cherry on the cake, does anybody know where this switch is placed on a Lenovo E540 Thinkpad machine ?
Thanks in advance for your help and answer !