possible system issues

So here is the issue I'm struggling with: After about a minute of smooth processing (70–130 fps), my games grind to an agonising 30 frames per second. Also, my wallpaper sometimes turns black. So far, I've tried a lot of things - plugging the laptop pc in, updating the drivers, setting the...

So I built my son his first gaming desktop of course we did it on a budget so most of the components for about through eBay however most of them are new. I got the rosewill d100 ATX gaming with the four RGB 120 mm fans with lights the motherboard is the tomahawk b550 and the GPU is the AMD 5700...