pc running game smoothly, then suddenly crashes. what should i do? i badly need help PLEASE.

hi ! so to start things off, my pc recently had it's motherboard replaced. i currently have a biostar a520m, a ryzen 5 3600 and a geforce rtx 2060. it also has a 16 gb ram and is running on windows 10 pro.

my problem is that my pc will run games smoothly for a while, but then suddenly it just shuts the game down. the games' graphics are buttery smooth, no lag whatsoever- and then it just shuts the game down. prior to this, my pc kept bluescreening and crashing so i gave it a nice system reset. after that, it stopped crashing but the games still shut down.

i've tried giving it a system reset (but not all the way, did a system reset while keeping my personal files and reinstalling windows from cloud), my drivers are up to date, my pc isn't too hot nor dirty- it has 6 fans already, my room is not that hot and it recently just got cleaned. i'm at my wit's end, i just want to play my games T T (plus this issue applies to other software, but doesn't shut down as quick as games do. i was able to use krita for at least half an hour.) i really really want to play my farming games soon.