pc cutting out

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i tried playing some games on my pc yesterday + after 5mins the pc cut out , it also done it 1 time last week as well (i thought it was down to maxing out video to fit native resolution of my new monitor , as soon a i droped resoulution on monitor i was able to play ut3 fine)
i tried running endwar + r factor yesterday + after 2-5mins my pc just cut out , the only way to get it back up + running was to either pull power lead out or press the on off button on psu
i have not had this problem before last week , the only thing thats been changed on pc was i done a clean install of xp with a dual boot of windows 7beta
my main pc is
AX78
amd phenom 9950 B/E
512mb Geforce 8800gt
Audigy 2
4gb corsair xms2 (4x1gb)
850w ezcool psu

[Lvcoyote]

Sounds like something is getting too hot.....

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Sounds like something is getting too hot.....

i was thinking along those lines i had noticed my HSF was getting a bit clogged with dust , i have just given it a bit of a clean + my idel temp has dropped 10'c
will try gaming later