Computer shutting down/resetting? (blue screen)?

I'd bought an ex corporate refurbished computer with windows 7, 4 gb ram, 160gb hard drive from a shop local to me. it kept resetting itself so i took it back and they gave me a different unit and it still did it then i realized it did not have enough power getting to it because it was plugged into a extension... show more I'd bought an ex corporate refurbished computer with windows 7, 4 gb ram, 160gb hard drive from a shop local to me. it kept resetting itself so i took it back and they gave me a different unit and it still did it then i realized it did not have enough power getting to it because it was plugged into a extension cord.(id never had this problem before due to having a low spec computer) i plugged it into a separate plug and all seemed fine but i downloaded plants vs zombies and after playing about 1 level it would reset itself and error report a blue screen appeared as it restarted. later on during game play my computer screen turned off then on again then my computer shut down completely then after i restarted it there was no error report.

thanks for any assistance guys x
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