problems when using 8800 Gts cards

on second thought technically the card is overclocked, but its a EVGA so it came like that out of the box

My 7800 GTX was a factory overclock - Gainward Golden Sample - but still it just popped due to a crappy power supply. When i rebuilt my latest machine, i went for a 750watt from a decent company - can't remember which, Antec i think - and it cost near £80, but it's better than paying out for a £200 graphics card again!
Also, this power supply has a trip in it so any spiking and hopefully it'll cut off before any damage is done.
Maybe you should think about replacing the power supply, just to be on the safe side?

If you decide to try a new Power Supply try Seasonic.
One from the best power supplys in the world is seasonic M12 80+ series
I have 700W 80+ for a few months and its perfect.
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Welcome to Seasonic USA
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M12 series power supplies are with detachable modular DC cables. Designed for Do-It-Yourself (DIY) system builders, gamers and Over-clocker enthusiasts, the M12 is available in three power levels, the M12-500, M12-600 and the M12-700. They provide stable power for high end, high performance graphics applications. Each model provides system builders the flexibility to create the most suitable combination of connectors to minimize clutter and optimize airflow in their PC systems.

It sounds like it could be a faulty PSU. Try replacing it. As other people have stated above, better than forking out $300 for a new card.