Help computer shutdowns every 10 mins

hello guys i have a problem my computer restarts during high processing loads what should i do i have already cleaned my cpu case and i have also tried reformatting my computers what should i do guys please give me some tips in how to solve this by the way my computer specs are
sempron am3 140 clocked at 2.70 ghz
1 gig ddr2 ram
on board video and a740gm-m ecs motherboard
