Since last week, after about 2 years of non-problematic behavior my 6870 started to produce artifacts on desktop (no in game problems yet). They started appearing during video playback (windows media player), sometimes during web browsing (Firefox), and sometimes on desktop with no windows opened right after windows start. They sometimes disappear, and sometimes crash the system (hard reset needed to reboot).
Once they did produce a strange effect, the screen shifted right and there was a visible connection between left and right parts of the desktop in the middle of the screen, after few seconds the system crashed. http://imgur.com/7RIHVuY
I started monitoring the temps of CPU and GPU and all are ok (46C CPU and 48C GPU) even when artifacts appear on screen.
There were no changes made to the hardware and software for quite a while now.