1. Check ur drivers are up to date
2. If u have done any overclocking get back to default settings
3. Temp is not that high but still blow the dust from ur graphics card and then check
4. If it is still artifacting then try another psu. U have not mentioned psu, if its a quality psu like corsair, antec or seasonic then i dont think its a psu problem.
If all of the above fail then its sign of a card which is about to die. This happened with my old 9800gt and it died in next few weeks