Laptop freezes permanently when closed in operation

[Volker Wysk]

Hello!

When I've closed my laptop, while Kubuntu is running, it fails to wake up 
again (when re-opening it). 

I get an empty, black screen, with the mouse pointer visible, but not movable. 
Everything is frozen. When I closed the thing while at the SDDM login screen, 
it again froze, but you get the login screen, with a (unmovable) mouse 
pointer, not a black screen.   

It doesn't make a difference, if the power is provided by the power cable, or 
by (full) battery.

My laptop is an Acer Extensa 2508. The OS is Kubuntu 15.10.

Any idea, anyone?

Thnx
Volker