Recently I bought a new PC, (first time I ever built a PC). After some difficulties I finaly made it, and I think heatsink is mounted properly. But my CPU is overheating (Ryzen 9 3900x). Iddle temperatures are around 50 degrees °C, sometimes even higher. In games when its supposed to be 60 degrees °C its around 80.
I cant go to store or servis, cuz my country has shops closed thanks to corona.
What should I do?
As others have said correctly.
Ryzen 3900x is a hot chip and often a normal temp idling is between 40-50.
80 degrees in game is fine, it is on the warmer side but definitely not be dangerous the chip that has a safety limity of 95 and will just throttle anyway.
If you want you can lower your voltage offset by 0.5 as many people, myself included, feel the motherboards over voltage the proessor.
So you would go into bios look for Vcore Offset and try -0.2 if it is stable at that offset then try -0.3 and so on but -0.5 should be fine. Lowering the voltage will lower the temperatures. The reason it shoots high is when the CPU does precission boost. Not to be confused with PBO which is precision boost override which is disabled in stock.
OTHER MAJOR POINTS:
i). Some software like iCue has been known to cause major issues causing the CPU to go mental in precision boost and get hot. I had it and taking it off drops my temp by 10c.
ii) Make sure you have the ryzen balanced powerplan selected in your windows 10. Press Win+i then search for "choose a power plan" .