Help! random restart's

[roughlad]

Built a system for the wife to play gws,surf ect, spec:
Intel Celeron Dual Core E3400 "LGA775" 2.60GHz (800FSB)
Corsair Value Select 2GB (2x1GB) DDR2 PC2-5300C4 667MHz Dual Channel
Asus P5QPL-AM Intel G41 (Socket 775) DDR2 microATX Motherboard

The system restarts randomly (checked temps there ok)
ran memtest, occt, burn test all pass.
tried a second psu/changed ram for spares.

Does anyone have any ideas what else could be causing this as it's starting to get on my nerves.

 

[roughlad]

formatted it 3 times, changed 2 spare hd.

 

[roughlad]

no blue screens just straight restart, happens anytime, i was playing gws for 30 40 min and fine then watched a vid on youtube and then it crashed. but its never died when running tests.