Randomly freezes PC

There is a problem and need help really understanding people. Start with configuration:
Motherboard Gigabyte G1 Sniper Z97
The MSI GTX 980
CPU i7 4790k
Operative DDR3 16gb
Don't know how useful this info, but still. It all started a couple of weeks ago, just after upgrading BIOS of the motherboard(don't ask why I did it, I also regret) the computer started absolutely randomly started to hang. That is, it's not a reboot and not even BSOD, just freezes and everything, and often does not even respond to the reset button, you have the power button for a few seconds to pinch that off. Before that was nothing like this. Live in a small town, took it to our local service, two days he has been here, then call me and say - you have one of two straps operatives buggy, it's all because of her. Well, OK(I basically originally, on what not hoping, bringing back PK, so just decided to pick it up while they were there nothing was done). Brought home in common with one strap started(the second they pulled out and gave it to me, they say it's because of it all). The computer worked a few hours and hung(unexpectedly). Now, how and when it happens. Most often he crashes on YouTube while watching a video, if it crashes at this point, the sound just loops( type RRRRRRRRR does:) ), may hang just on the desktop when I do nothing at all, but it was not so often. In games the situation is ambiguous in the game Darkwood, do not demanding to resources, the computer hangs quite stable, as well Sizikova sound and reacting, while Far Cry 5 for 40 hours of the game never hung. I don't know if it was a happy coincidence or there is some sort of addiction, but in this context I last 2 weeks only to farik and drove, fearing even to launch chrome and go to YouTube. Once more I will say the obvious, with the temperature of the processor and video card everything is normal and it is certainly no overheating. In General it seems to have painted everything that seemed important, if you have questions and someone responds, ask, try to answer everything