Artifacts appear after playing video for a while

[TigerLord]

I now have a problem which I've never faced before since I started building computers 10 years ago.

The problem is as follow

-Artifacts appear on the image of the video being played, as well as around the mouse cursor, after video has been playing for a while. It seems to be random, though it happens more with H.264 material.

-Once the artifacts appear if I try to do any action the computer will lock and freeze. Only fix is a reboot.

-This problem does not appear when I game. Example: running AoC all on maxed settings @ 1680x1050 without a single issue. I thought artifacts usually indicated memory failure on the GPU, but wouldn't it happen also when I game?

-I've tried various players but it didn't fix the issue.

What I tried to fix the problem

-Put the computer back to clock speeds
-Loose timings on the RAM
-Increased fan speed of the GX2 via the EVGA Precision Tool

I realized it's not much but the symptoms don't make sense. If it were memory failure it would do this when I game. H.264 video is hard on CPU but I have a Q6600 and it is nowhere need 100% load when I play them. The problem also appears on stock, so it ain't CPU. My OC was 9+hours stock stable and the rig is watercooled (both CPU and NB, SB has custom HSF)

Anybody ever heard of this? Can this be software related? I've got latest 64bit 175.16 forceware drivers.

I could really use some help this is pissing me off!