Earthwatts psu causing system crash

Here is my config:

Antec Sonata III box
Motherboard: Asus P5Q-E
Processor: E8500 overclocked to 9.5x400 (3.8 GHz)
CPU Fan: Noctua NH-C12P
3 Hard Drives in AHCI ATA:
1 150GB
1 750 GB
1 Seagate
1 Reader / DVD Burner
4 GB Ram DDR2 800 Kingston Dual Channel
Graphics Card HD 4670 512 RAM
2 External Hard Drives 1TB each (Western Digital) in eSATA
1 Wifi card (PCI-e)
and different USB devices like webcam, keyboard and USB mouse

Here's my question!
Since I build the computer last year, it regularly crashes in games, whether Devil May Cry or Need for Speed Shift. I put all Microsoft systems on this machine from XP to Windows 7 (the one I have right now), my drivers are all updated and my bios too, and yet it crashes! And the crash in good standing, frozen on the screen play, its blocked, and requires Reset! And sometimes reboot automatically after the reset!

It occurred to me the idea to end solutions I must admit, change the psu, I do not see that it might allow me to add another 4670 Crossfire in the near future. According to an estimate from Antec, I will consume 400 watts, so the EarthWatts from Sonata should survive for now....

Making a crossfire of 4670 makes no sense, rather go for 4870. Otherwise does it crashes without overclocking too? Have you tested your ram? Estimated by the 400w Antec seems odd, a 4670 consumes very little, I think you can even consume between 200 and 250w

Thank you for your reply. Regarding the Crossfire, I hesitate, but your advice will be welcome, for example, why not pair 2 HD 4670? And was in no hurry, it is worth the wait chips compatible DirectX 11? Without overclocking, there's the same crash, and regarding the RAM I have not tested. Which software do you advise me?

Yes, can not exceed 250W with your configuration. The EarthWatts is manufactured by Seasonic on the same basis as the S12II. Difficult to do more reliable. Perform a memtest of your RAM, and a little later down the frequency of your processor, I think it owes more to come. Is your 4670 in default settings with less frequency?