How to troubleshoot random Windows freezes-crashes?

I have this problem since I can remember :)
Apparently randomly, my Windows 10 freezes, requiring an hard reset.
The freeze is totally random: there aren't any signs before like slowness or mini-freezes.
The image on screen freezes on what it was viewed; if speakers are on, a somewhat white noise starts: it's pitch high and redundant. Other times the last 0.5-1 seconds of audio are repeated in loop. Others the pc simply restarts itself. No action is allowed: the mouse power off lights, and no keyboard shortcut can be runned, neither Ctrl-Alt-Canc.

These freezes occur once in a 2-3 days, with apparently no strong link with what is running; however, most times I'm playing 3D games or watching videos via browser. Still, freezes can occur in totally idle Windows, without any programs running.
I suspected it was a graphic card problem; however, little time ago I changed it but crashes still are here. Problem was there with Windows 7 and 8 too, when I had them on same hardware.

Event viever shows not any clue, as far as I can tell: the only critical event is Kernel-Power, probably caught when I restart by restart button.

Question is how can I investigate these freezes, to get clue what componet is failing. Outside of freezes the computer is running very well, also in high load situations like playing high demanding games. For this reason, I suspect is not a temp problem, but I'm open to investigate this way, if reasonable.

Thanks for your time dear Superuser users,
Angelblood_6x

EDIT: forgot that, everytime the system crashes, boot time significantly rises, going from 19 seconds to 1 minute (logged by 360 Total Security). BIOS load is also slowlier, with increased time passed on POST step. Then, the whole system is a bit sluggish after Windows logon, compared to a "normal" boot, and it takes some more 30 seconds to regain good working speed.

Answer

I have found an answer and put here for reference. I did, as suggested, memtest86+, wich found no problems at all after some hours. But, very oddly, when I finally DOWNCLOCKED my RAM under suggested FSB, I had a very stable system. Can't explain this.