Have you tried swapping the RAM and/or trying 1 single module at a time?
Also, it could be the PSU that it's failing. Those things are the ones I'd check if I were you.......update the BIOS as well, nForce don't like Quad-Cores from what I've red in magazine articles.
Also, it could be the PSU that it's failing. Those things are the ones I'd check if I were you.......update the BIOS as well, nForce don't like Quad-Cores from what I've red in magazine articles.