I think the screen light's battery has been dead.
(When I say about "flat battery", can I also say "the battery is out" or "the battery is run out"?)
To solve this problem, I connected the PC with a TV monitor with a HDMI cable.
Thanks to that, I enjoy surfing the net on the larger screen. lol
But, I can't watch TV while doing that.
So, I need to go to an appliance store to have it repaired soon. :-<