In the first instance I would say graphics drivers, but you've already done that. Next step I would try is re-seating your graphics card - maybe give the fans/vents/ports a bit of clean at same time.

If that doesn't work it may be a fault on the card itself - I had similar issues with a Radeon card a few years back and it turned out it had bad memory chips on it that failed only a few months after I got it.