Graphics Issues? Greenish pixel's on most blue shades.

[Ilwrath]

That's a strange one.  
Graphics card fault is a possibility, though I suspect it's probably something more innocent.  

Some troubleshooting steps to consider, if you haven't already:
What happens if you change desktop resolutions?  Color depths?
Any Windows updates or ATI video driver updates installed recently?
Also, is the monitor hooked up by DVI or VGA?

[Ilwrath]

Well it isn't the latest drivers though that shouldn't be the issue as 6.12 was working fine for over a year

yah, that's fine.  I was just trying to make sure you didn't update the drivers last week and shortly thereafter the problem developed.  If the newest drivers cause your system to blue screen halt, though, that is a bad sign.  There may be faulty or not totally compatible hardware.

I suspect a RAM or RAMDAC failure (for VGA) - both non-servicable), probably you're best off looking for a replacement gfx card.

That was one of the things I was suspecting, as well.  Shouldn't a faulty video card RAMDAC have caused the visual glitches to manifest differently at different resolutions and color depths, though?  

Just for the heck of it, it might be interesting to try a Linux Live CD on the box, just to rule out the chance of it being related to Windows drivers.  Of course, either way, switching the video card would likely cure the issue as Windows would load new drivers upon detecting a different card.  ;-)

[Ilwrath]

Ok it seems to be a Windoze related issue (surprise, surprise)

drivers...  personally, my advise would be:

1) Install the Aug 2009 DX9.0c redist from microsoft.com.
2) Go on Microsoft update, install any update it detects for ATI video.  
3) Download and install the latest ATI driver package.  (Don't reboot after this step, even if the system asks you to.)
4) Go into device manager, delete everything under Display Adaptors.
5) Now reboot.  Let Windows sort out the drivers, detect the 'new' hardware and pick whatever the heck drivers it feels like.  

Sometimes letting Windows have its way is the only way to have a functional install.