Here are some indicators for you as a pc noob to use another time

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My screen is black, but my sound is fine
First off make sure your monitor can run at the requested resolution, you can try and lower setting. To make sure thats not the problem.
Check your video card drivers make sure you don't have old versions, sometimes because graphic cards developers creates multiple drivers for the same series the old versions will be better, google it and you might come across something.
My screen flickers along with my sound/random crashes
Most likely your motherboard, normally this occurs with a motherboard that is either broken or cheap. Not much to do here sometimes it can be fixed with a trick but most likely not.
My Pc shutdown randomly when I play
This error can only mean two things:
your CPU gets too hot or you don't have a powerful enough power supply.
Everything is fine but after 10 min-1 hour my game lags a lot
This is the result of bad programming of either your driver or your game, the reason this occurs is because you have a memory leak and after some time you will run out. I had this problem in SC2 because my graphic card was broken. If this occur try having task manager on your second screen while you play so you can see the memory usage.
Now for true pc's the price of fixing these problems are not that high:
Here is a list of good replacement value hardware that took me 10 min to find:
as I am one ban away from perm ban I am not going to risk getting ban for advertising.(write me a PM if you want the name)
(case with 500W power supply) -48£
very solid motherboard - 181£ (a bit expensive but I have never had a PC this stable)
Graphic card - 173£
CPU(that works with motherboard) - 100£
8GB DDR3 ram - 90£
2000 GB hard-drive - 65£
I put these in to give an idea of how much it costs to replace.