Random Crashes Issue

Hey there,
for a few days I am experiencing crashes on my Windows 10 desktop PC. I couldn't really find out any trigger yet and there is no BSOD. It could be possible, that it crashes more often, when I play graphic intense games, but it also crashed while just listening to spotify. Everything just stops working from one second to another and my monitors are freezed. Also the sound is freezed, so there is a weird artifact repeating until I reboot my pc by pressing the power button for a few seconds. How can I fix it and what information do I need to provide to you, so you can help me out? Thank you so much in advance!
I built the PC by myself 3 years ago and got a new graphic card for one year now, because the old one was broken.

Processor: Intel Core i7 4790k (not overclocked)
Mainboard: ASRock Z97 Extreme6
Grapic card: AMD Radeon RX Vega
Windows Version: 10.0.19042 Build 19042

What I tried until now:
- I checked Windows update and I installed the latest updates.
- I updated all the drivers on my pc with driver easy.
- I got no violations with "sfc /scannow" and did the recovery process with "DISM.exe /Online /Cleanup-image /Restorehealth".
- I did error checking on my hdd and ssd and had some issues there but Windows fixed it.
- I did "mdsched.exe"
- I deleted all temp files of Windows

What else can I do? Could it have something to do with the power supply or mainboard?
Thank you for your help!