You may have used non-static cloths but did you earth yourself before touching components? Maybe you zapped the graphics card when you removed it or put it back. Also, unless you are in a dusty environment, there is no need to do a 'regular 6 monthly clean'. After 6 months there shouldn't be enough dust to be concerned about. I reckon every 18 months/2 years is enough and even then only use the air duster without touching the components. The more often components are disturbed the more chance of damage. Might need a new graphics card.
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