Check the website of the RAM manufacture and see what the voltage specs are.
I had the same problem with my Gigabyte motherboard and a 465W power supply.
After spending the money to replace the power supply, the problem persisted.
Checked the Mushkin website and found that 2.5V was the MINIMUM operating
voltage of my RAM, up to 2.8v. The machine ran fine with one stick at 2.5V,
adding the second stick crashed it repeatedly. Increased the voltage to 2.7V
and its been stable ever since.

Fitz