SOLVED
Hi everyone,
Problem is not with a video card and is has nothing to do with video drivers. I think it has something to do with a motherboard.
Before this solution I tried everything - renewing video drivers, deleting windows updates, I even installed new system coolers, tested random memory for errors - nothing helped.
I have Gygabyte GA-MA78G-DS3HP. What you want to do is download latest mother board drivers from GYGABYTE site:
http://www.gigabyte.com/support-downloads/download-center.aspx?ck=2
I don't now about the other models, probably you can find something similar on google.
I'm not sure which one of them did the trick, I recommend installing them all - chipset, audio, networking, it never hurts to renew your system drivers.
Finally after 6 months of crashing I can finally enjoy full system performance. Good luck.