PC screen is all black

Hey! So I needed to work on my PC today and when I pressed the power button, it made the sounds it usually does. It showed me the LG signs and all that but then, the screen went all black. I can hear the fan running, and all the sounds that I hear usually. I tried re-plugging every plugs and started the computer again. But the screen was black again. I have so many valuable files and photos saved in the computer. There is no backup... and I really need to back my files safely.

Can anyone tell me the problem (why the screen is all black) and what I can do?
Or if you said how to get back my files, that would be great as well! Thanks!