Why won't my pc turn on?

There is a problem with opening my pc, first is the keyboard, when I finished assembling the pc, my keyboard is faulty, when I turn it on it works normally but after using it for a while I can't type, I have done everything I can and don't know what the reason is, second is that when I turn on my screen it shows no signal, I have to turn it off and restart it many times to get it working and the refresh rate is very low even though it was initially customized normally, third is most recently about the case, when I turn it on it still shows the window icon as usual but after running it is a black screen, I can't do anything even though I can still press the key combinations but it is still like that all the time, please help me because this is my passion, thank you