Concerns on Home School Software

I have a HP Probook 4430s that I’ve been using for about 6 months. I had to replace the mainboard once. Recently I have been experiencing the screen turning really dim randomly. When it first happened, I was using it normally then I put it to hibernation and packed it in my bag to leave home. I drove a motorbike. After I got home a few hours later, I turned on my laptop but the screen was really black whilst the laptop was still running. So I had to force shut down. After an hour or so, I turned it on again and the screen worked perfectly. However the next two nights, whilst I was still using the laptop with normal functioning like surfing internet and watching videos, my screen just suddenly turned black again when I could still hear the video playing. I tried to manually shut it down and turn it on but again the laptop worked but the screen remained black. Weird thing was after that the symptoms didn’t occur again until today when I packed it in my bag and left school on the motorbike and the same thing happened again. But this time I flashed a torch onto the screen and I can see dimly the outline. It seemed that the screen was still on but it was so dim and dark that I couldn’t see it normally without using the flashlight. Again I turned it off and left it there for a couple of hours and now it’s working perfectly.
I don’t know what the possible causes are. Since the laptop still works only the lcd screen turns extremely dim, could it be because of the defected screen or the inverter’ Or is it caused by defects in software’ Any help would be appreciated