Computer not staying on?

Alright, i noticed a few weeks ago that my computer was not staying on, like it would restart at random. I ran anti virus software (Avira and Mbam.) And i also ran tons of other things in a attempt to fix it, after a while i just got fed up and formatted my drive and did a complete re installation of windows 7 64x. And it is still restarting, not nearly as often but it still does it... I am not sure but i think it is a hardware error which i know nothing about... Any suggestions?

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System Information
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Operating System: Windows 7 Ultimate 64-bit (6.1, Build 7600)

System Manufacturer: HP-Pavilion

BIOS: Phoenix - AwardBIOS v6.00PG
Processor: AMD Phenom(tm) 9150e Quad-Core Processor (4 CPUs), ~1.8GHz
Memory: 4096MB RAM
Available OS Memory: 3966MB RAM
Page File: 1842MB used, 6088MB available

DirectX Version: DirectX 11