iMac Graphics Crash

newbie here. imac doing this.




imac 21.5" (mid 2010) 3.06ghz/16g ram/500g hd. ex-display model (which in may suggest tech wizards) bought 6 weeks ago. came snow leopard , screen crash occurred more once on day one. upgraded os x , stable few weeks reassured same screen problem has recurred recently.
screen apparently randomly, i.e. when sitting untouched, when online , when mid-game.
have:
-verified/repaired hd (no probs identified)
-repaired permissions
-reset nvram
-run fan control app (all 3 fans respond increased revs, temp max 55c)
-run gui memtest ("rember") = no probs ram
-then clean install of os x , repeated of above
-run apple hardware test (basic = no probs found, more complex = has been unable complete issue has developed on 3 consecutive attempts mid-test)

forum wisdom i've come across far has left me unclear whether hardware or software. clean install suggests hardware, apparently highly unlikely.

no apple care extended retailer warranty theoretically covering naturally anticipate avoid taking on. plus want make case when phone them exhausting can myself hoped out there might able offer other interpretations of problem or suggestions.

kinda out of ideas here.

thanks.

 

same here except imac (2009 2.93 c2d) fine on leopard , snow leopard. upgraded lion, boom. issues non-stop. i've run same things , nothing comes up. i've been deleting applications day have been coming on kernel panic logs. thing seem gather when have browser open. rather safari, chrome, or rockmelt. other time, see crashes or kernel panics. played minecraft earlier because if it's graphics card related, surely minecraft push crash faster idling browser. nope. minecraft played fine hour. uninstalled flash , seems ok far. (chrome somehow had 2 versions of flash installed) drives me nuts. re-seated ram (tested earlier) i'm out of ideas. comes we're both missing.

 

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