Here are some of the most common scenarios that you might face:
My keyboard lights up, and I hear it turn on, but I cannot see anything on the screen?
If your keyboard lights up, but there is no display, then that means that the system is getting powered up, but the GPU might having problems, your internal disk drive is corrupted or damaged, your display is damaged, or LVDS cable might be loose (This cable hooks your motherboard to your display).
Lastly, there is a chance that this may be a software issue if this happened recently after a Windows update, or a driver update on your computer.
When I hook it up to an external monitor, I can see a display, but not on my laptop display
Displaying on an external monitor helps you identify whether or not your GPU is failing. A failing GPU, no matter what display you connect to, wouldn’t display anything. This still doesn’t root out a driver issue with your display, but you can be reassured it is either a software issue or a hardware issue at this point (i.e. LVDS cable loose as described above, or a damaged display).
When I hook it up to an external monitor, I still don’t see anything
Just like the previous problem, this is also a case of driver issue, but also look at your settings and whether or not they are optimized for a dual-screen setup. (Assuming your laptop screen also isn’t black). Check the connections and also the cables. More often than not, a bad cable can also cause a lot of problems that you won’t identify till the last moment.