I built this computer in June. Since then, it's pretty much had no issues, until yesterday. I had been playing a game (Divinity: Original Sin 2) without issues for around 20 hours over the two weeks prior to yesterday, but yesterday the game froze and crashed to desktop. I could still hear talk on Discord while it was frozen. It did the same thing 3 or 4 more times over the next 10 minutes. After being stable for a while after that, I started getting white flashing lines appearing at random on the textures in-game. The game soon crashed again. Today, I tried playing Forza Horizon 3, and it was absolutely fine for an hour, but then froze and crashed to desktop. I was trying to type a web address into Firefox and my computer locked up, went to a black screen for around a second and then came back and the text I was typing appeared. The computer has also locked up when loading AMD Ryzen Master and one other time when doing light computer work, both of which required me to force shutdown my computer.
I have ran several tests using BurnInTest, testing all components, and the tests came back with zero errors.
Ensured all drivers are up to date.
Scanned using sfc to repair corrupted files.
Done a full computer scan using Windows Security.
Had HWMonitor running while gaming. (Around 40c for CPU and 60 - 70c for GPU).
As said, everything was fine up until yesterday, except for the very occasional tiny lock up. My instincts tell me it's either a GPU or PSU issue, but I'd like some further help.