I pressed a key then the laptop turned the screen black but it's on

[teresia.yieldplus.uk]

F8, f9 f10 then enter

 

[Ralston18]

Make and model laptop? What Operating System?

Does the screen still stay black after powering off and on?

You may have invoked some screen saver or power saving function; more information is needed.

 

[webworkings]

You could have also hit a key to switch to an external monitor, even though you may not have one connected. Is there a key on the computer that has what looks like two little monitors?