glbv, ever dusted your machine? To me it just reminds me far too much about physical damage to the graphics card. What I recommend that you do is that you either try out some other games or applications that require a bit of work from your graphics card and see if you get similar artifacts.

If you do, then I suggest that you hand over the graphics card to a rapairshop and ask them to replace it if it can't be repaired.

Hopefully I'm wrong about my suspicion, but you never know...