I had a bfg 6800gt start artifacting on me and about 10 seconds later the system locked up. I restarted and got artifacts at every screen. I then tried goin into the bios and still saw artifacts. I then tried my old gf5500 and there were no artifacts. Luckily my card was covered under bfg's warranty. My guess would be that yours is dead. I'd try another card first. If you get the same thing maybe a different power supply or monitor. I'm not an expert at this but elimination is the best thing i can recommend. Also, with the thermalpaste, that doesnt sound good as it should probably be on your core.