Coming back to this after some time and some problems. I wrote my last post too quickly without any tests. Moderators, feel free to move this thread to a different place.
My old system was: AMD 2700, MSI X470 Gaming Plus Max, GTX 1060, G.Skill Aegis 2x8 GB, Intel 660p M.2 1TB, KingSpec P3-1TB SATA, Xilence XP1200.
I have build it last January and has been running 24/7 for a year, almost without any problems. I only remember one blue screen error and two or three game crashes, including the last fatal one.
After the last post I tried to connect the KingSpec 1TB disk (which was my overnight backup disk) and I got a BIOS lock screen with an A2 error. Search indicated that the error is related to disk/SATA. After many ways and checked on different systems the disk was indeed completely dead.
Within a day I started getting various blue screen errors and sometimes the applications crashed. The frequency was at least once a day, usually more, and I have seen it happen three times in a row and even at idle.
After this I checked the memory with memtest86 and after more than 3 passes and no errors I quit.
Then I switched the power supply with an older one and the situation remained the same. Another memory test and it gave me an error before the first pass (I stopped the test).
Afterwards I started with an external disk loaded with Windows 10, same story. I also checked the Intel disk with Intel Memory and Storage Tools (I completely erased the disk and made a full diagnostic scan, no errors, but it needed a firmware update).
So I made a new installation, same situation, the errors seem less frequent. Made another memory test, full test passed (4 passes) without any errors this time.
I have ordered new memory believing it would solve my problems and a new power supply as the older one had short cables, from the era when power supplies used to go on top. I hope to get them by next weekend.
I want your opinions on what went on and what is going on. Xilence power supply is my main suspect for the main failure although it does not explain the memory error I got. I believe I have memory errors now or incompatible memory. Then again it could be a faulty disk? I also like to believe my cpu is still good. Is it possible that Windows was badly burned to the USB? No other tests were done since the system is not stable.