It definitely sounds like the graphics card is overheating or the card is damaged. Is the fan spinning? Is there something against it preventing the fan from working? Is air flow to the fan on the card blocked? Is the card overclocks or modified from it's original state? Those could be causing the issue.
I face exactly the same problem at the moment. The "fun" part is, that artifacts shows up only during the "low performance" state, ie when comp is doing nothing or web browsing or something line this. During games, 3DMark06 or 3DMark11, when GPU is in full load and one would really expect some problems, everything is perfectly fine and there are no artifacts at all.
When I removed GPU and let i5 core GPU to work, artifacts disappeared. So it seems like GPU problem. But still, in the first post there is information that GPU change doesnt helped AND if GPU is the case, why it doesnt freeze or show artifacts during the tests/games?
Every good idea will be appreciated.
CPU: intel core i5 2400 3.1ghz
GPU: ATI Radeon HD 6800 1GB
RAM: Kingston Hyperx 1600 2x4 GB
PS: Fortron 550W
SYS: Win7 x64 Home Premium
I'm having this same problem. No artifacts in games, no errors in stress tests, however, when browsing the web or on the desktop, I get these small square pixels. Usually red or green, has scratches in them, the exact same symptoms.
CPU: Phenom II X4 3.2 GHz
GPU: Radeon HD 5970 2GB
PSU: 850W Corsair TX
RAM: 8GB DDR2
SYS: Windows 7 x64 Ultimate
Drivers are up to date.
The problem started happening right after I updated to... Catalyst version 12.3 I believe? This leads me to think it's a driver problem, hopefully. My cards out of a warranty, and the problem only happens when I'm not doing anything.